Chlorella sp. microalgae are often cultivated for various purposes such as medicines, cosmetics, and alternative energy such as biodiesel, bio-crude oil. Different concentrations of nutrients in culture medium can give different effect on population growth and essential content of Chlorella sp. One of them is the concentration of nitrate and phosphate. In order to increase the biomass produced, it is necessary to enhance its growth with another medium that that are cheaper and easier. Urea and TSP was used as source of nitrogen and phosphate element in various ratio for the cultivation at flat plate photobioreactor. Among the process conditions tried, cultivation using urea and TSP fertilizer medium in ratio 2:1 (CI) was considered as the optimum composition that resulted in highest cell density, 4.28 × 107 cells/mL. Then, medium in ratio 4:1 (C2) which was 3.10 × 107 cells/mL and the lowest cell density found in ratio medium 6:1 (C3) which was 1.65 × 107 cells/mL. Medium with low nitrogen content had the highest cell density. The temperature culture during cultivation was in the range of 25 - 26 °C and pH value was in the range of 8.3 - 8.7. Temperature and pH culture during cultivation are still in optimal conditions for the growth of Chlorella sp.