In this study, the effect of temperature on growth and some reproductive parameters of guppy Poecilia reticulata were investigated. And 19, 21, 22.5, 26, 29, 32 and 35°C water temperature treatments were used on newly hatched fry and gravid females for 11 days after parturitions and several days starting from the 16th day after first parturition until second parturition, respectively. Survival rates of heat treated fry were lower in the high temperature groups of 29°C and over than the low temperature groups of 22.5°C and lower. Same trend was observed for gravid female which all died in the temperature groups of 29°C and over. Guppy fry grown better at temperature between 22.5-26°C and the gravid female guppy produced high number of fry at temperature between 21-26°C may support the hypothesis that an ontogenetic reduction in temperature optima with increasing size for growth and the optimum temperature for growth broadness as body increases. However, size and sex dependent optimum temperature range for optimum growth and reproduction of guppy could be in question.