Smilisca phaeota tadpoles were exposed to four sublethal concentrations (0.1, 1.0, 10 y 100 μg/l) of chlorpyrifos insecticide, in order to test the effects on growth rate and the time spend to reach the metamorphosis. Were used 36 tadpoles (six replicates for each treatment), between the Gosner stages 25-26, which were individually placed into 100 ml glass beackers with 80 ± 3 ml of solution. For the each individual, the total length (TL) was measured at the third and eighteenth days, and at the climax of metamorphosis (stage 42). The main growth inhibition was observed at metamorphosis, with a reduction in the mean TL of 14 and 17% in the treatments with the higher insecticide concentrations, compared to the control treatment. At the third day of exposure, there was a 13.3% reduction in the size of the tadpoles exposed to the highest concentration (100 μg/l), compared to the control treatment. In contrast, at the eighteenth day of exposure, there was no significant effect on tadpole growth, for any of the treatments. Therefore, is possible that the both initial and final stages of larval development are more affected by insecticide exposure and the time to complete metamorphosis was also affected by chlorpirifos exposure. The tadpoles exposed to the two highest concentrations of insecticide took more days (mean 43 days) to reach metamorphosis.