Understanding of concepts and scientific reasoning are an important components of the Physics learning process. One of the importance of understanding the concept and scientific reasoning is facilitating students in understanding and applying concepts obtained for everyday life. This article aims to describe students' understanding of concept and scientific reasoning on Static Fluid topic. This research used mixed methods explanatory design with 31 students of class XII IPA who have obtained Fluid Static topic. The instruments used are 10 items of essay for conceptual comprehension and 20 multiple choice items justified for scientific reasoning with substantial reliability in order, ie 0.702 and 0.745. The results show that students still have difficulty in understanding the concept of Fluid Static and still have a low scientific reasoning. Students' understanding of hydrostatic pressure sub topic is 18%, Pascal's Law of 21%, and Law Archimedes of 2.2%. Scientific reasoning aspects used in this research are mass conservation reasoning, proportional reasoning, variable control, reasoning probability, correlation reasoning, and hypotetical deductive reasoning. Sequentially, the low level of students' scientific reasoning on Static Fluid material in each criterion is indicated by the following percentages: 24%, 40%, 34%, 25%, 48%, and 20%. Based on the results obtained, that the difficulties of students in general exist on the determination of factors that affect the phenomenon of each sub-material. Abstrak: Pemahaman konsep dan penalaran ilmiah merupakan komponen penting dalam proses pembelajaran Fisika. Salah satu pentingnya dari pemahaman konsep dan penalaran ilmiah adalah dapat memberikan kemudahan siswa dalam memahami dan mengaplikasikan konsep yang diperoleh untuk kehidupan sehari-hari. Artikel ini bertujuan untuk mendeskripsikan pemahaman konsep dan penalaran ilmiah siswa pada materi Fluida Statis. Jenis penelitian ini menggunakan mixed methods explanatory design dengan subyek penelitian 31 siswa di kelas XII IPA yang telah memperoleh materi Fluida Statis. Instrumen yang digunakan dengan 10 butir soal esai untuk pemahaman konsep dan 20 butir soal pilihan ganda beralasan untuk penalaran ilmiah dengan besar reliabilitas secara berurutan, yaitu 0,702 dan 0,745. Hasil penelitian menunjukkan bahwa siswa masih mengalami kesulitan dalam memahami konsep Fluida Statis dan masih memiliki penalaran ilmiah yang rendah. Pemahaman konsep siswa pada sub materi tekanan hidrostatis sebesar 18%, Hukum Pascal sebesar 21%, dan Hukum Archimedes sebesar 2,2%. Aspek penalaran ilmiah yang digunakan dalam penelitian ini, yaitu penalaran konservasi massa, penalaran proporsional, kontrol variabel, penalaran probabilitas, penalaran korelasi, dan hypotetical deductive reasoning. Secara berurutan rendahnya tingkat penalaran ilmiah siswa pada materi Fluida Statis di masing-masing kriteria, ditunjukkan dengan persentase sebagai berikut: 24%, 40%, 34%, 25%, 48%, dan 20%. Berdasarkan hasil yang diperoleh, bahwa kesulitan siswa secara umum terdapat pada penentuan faktor-faktor yang berpengaruh pada fenomena masing-masing sub materi.

Scientific literacy is one of the basic competencies that must be possessed in the XXI century. These competencies include explaining scientific phenomena, designing and evaluating scientific investigations, and interpreting scientific data and facts. These three competency indicators must be embedded in students to help them to solve problems and give the best responding to issues especially science issues, as well as "flat earth theory". The purpose of this study was to describe students' scientific literacy competencies in responding to scientific issues "flat earth theory" and their indications in responding to issues. This research is a description research by questionnaire method and interview. The research subjects were 92 students in several high schools in Malang. The questionnaire results show that 95.65% of students rejected the "flat earth theory". Among those who rejected the theory, 20.97% of respondents did not conduct an investigation to conclude the information of the theory. The interview results of this research indicate that students only relied on initial knowledge or initial information to conclude the issue.