Penelitian ini bertujuan untuk mengkaji dan menganalisa besarnya peningkatan daya tahan membran sel eritrosit dan jumlah sel eritrosit akibat latihan aerobik intensitas sedang. Penelitian ini merupakan penelitian eksperimen semu dengan pendekatan kuantitatif, serta menggunakan rancangan pretest and posttest design. Populasi dalam penelitian ini adalah mahasiswa jurusan PKO FIK UM, dengan tehnik sampling menggunakan purposive sampling, serta jumlah sampel sebanyak 20 orang. Variabel bebas dalam penelitian ini yaitu latihan aerobik intensitas sedang. Latihan dilakukan dengan frekuensi 3 kali perminggu, selama 8 minggu dan durasi latihan 30 menit. Variabel terikat yaitu: 1) daya tahan membran sel eritrosit, dan 2) Jumlah sel eritrosit. Data variabel terikat pretest dan posttest dikumpulkan dengan teknik memeriksa darah vena yang dilaksanakan di laboratorium klinik Diagnostik Bromo Malang. Analisis data menggunakan teknik Uji t paired sample t test dengan menggunakan α 0,05. Hasil analisis data penelitian menunjukkan bahwa Fragiltas Osmotik sebagai indikator variabel daya tahan membran sel eritrosit Pretest 0,46±0,02% dan postest 0,43±0,02 %, P-value 0,029 α (0,05) sedangkan variabel jumlah sel eritrosit pretest 5,4580 ± 0,223 juta/uL dan postest 5,6230± 0,142 juta/uL,. P-value 0,021 α (0,05). Hal ini dapat disimpulkan bahwa terdapat peningkatan yang signifikan daya tahan membran sel eritrosit dan jumlah sel eritrosit akibat Latihan aerobik intensitas sedang.Increased endurance of erythrocyte cell membrane and erythrocyte cell number due to moderate intensity aerobic exerciseAbstractThis study aims to examine and analyze the magnitude of the increase in the endurance of the erythrocyte membrane and the number of erythrocyte cells due to moderate-intensity aerobic exercise. This research is a quasi-experimental research with a quantitative approach, and uses pretest and posttest design. The population in this study were students majoring in PKO FIK UM, with a sampling technique using purpusive sampling, and the number of samples was 20 people. The independent variable in this study was moderate intensity aerobic exercise. Exercises are carried out with a frequency of 3 times per week, for 8 weeks and the duration of the exercise is 30 minutes. The dependent variables are: 1) the durability of the erythrocyte cell membrane, and 2) the number of erythrocyte cells. The dependent variable data of pretest and posttest were collected by using the technique of examining venous blood which was carried out at the Bromo Diagnostic Clinic Malang. Data analysis used the paired sample t test technique using 0.05. The results of the analysis of research data showed that Osmotic Fragility as an indicator of the durability of the erythrocyte cell membrane. Pretest 0.46±0.02% and posttest 0.43±0.02%, P-value 0.029 (0.05) while the variable amount erythrocyte cells pretest 5.4580 ± 0.223 million/uL and posttest 5.6230 ± 0.142 million/uL, P-value 0.021 (0.05). It can be concluded that there is a significant increase in the endurance of the erythrocyte cell membrane and the number of erythrocytes due to moderate-intensity aerobic exercise.