The growth differences between cyanobacteria strains Leptolyngbya HS-16 and HS-36, which were incubated in temperatures 20°C, and 50°C had been studied. Those strains were isolated from Gunung Pancar (Leptolyngbya HS-16) and Maribaya (Leptolyngbya HS-36) hot springs which were in West Java, Indonesia. The water temperature of habitats was 69°C (Gunung Pancar) and 42°C (Maribaya). Those strains were grown in batch culture for 7 days in BG-11 medium. Biomass weight during growing of strains Leptolyngbya HS-16 and HS-36 was the parameter of the growth. Observations were done from day-0 (t0) until day-7 (t7). The results showed that there were differences in growth curve of those strains. Biomass weight in day-2 (t2) of Leptolyngbya HS-16 incubated in 20°C was higher than biomass weight in day-0 (t0), however biomass weight in seven days of Leptolyngbya HS-16 incubated in 50°C was lower than biomass weight of day-0 (t0). Biomass weight of Leptolyngbya HS-36 incubated in 20°C was lower than biomass weight of day-0 (t0). Biomass weight in day-3 (t3) of Leptolyngbya HS-36 incubated in 50°C higher than biomass weight in day-0 (t0). Leptolyngbya HS-16 and Leptolyngbya HS-36 that were incubated in 20°C and 50°C went through adaptation (lag) phase. The color of Leptolyngbya HS-16 culture, which was incubated in 20°C, changed from emerald green color (t0) into leaf green color (t7). It also happened at the color of Leptolyngbya HS-36 culture, which was incubated in 50°C it changed from brown ochre color (t0) to nougat color (t7). Growth curve data showed the highest rate of growth in lag phase of Leptolyngbya HS-16 was in 20°C and Leptolyngbya HS-36 was in 50°C, but their color of cultures were changed because of the metabolic reaction.