Science process skills could not be separated from the process of conceptual understanding in teaching-learning of science and applied science. The skills needed to be identified and discussed as skills which were implementable in many subjects. The assessment on students' skills was influenced not only by the ability to use these skills, but also by the knowledge of a particular subject in which the skills were used. The aim of this study was to analyse students' science process skills by using Testlet instrument. The science process skills were analysed from 226 students studying in three different schools. The Testlet instrument in this study was designed in the form of multiple choices. The indicators of science process skills in this study consisted of conceptual knowledge, observation, controlling variable, interpreting data and drawing conclusions. The results obtained in this study were that the students' completeness on conceptual knowledge was 71%, on observation was 39.7%, on controlling variable was 29.4%, on interpreting data was 35.7%, and on drawing conclusion was 29.7%.