Zooplankton in small tropical lakes has been little studied and its variation during the year may respond to different factors. In this study, the zooplankton of a small neotropical lake was studied at different times during one year and compared with changes in the lake conditions and in phytoplankton composition. The lake stratifies from March until September, and mixes during the hemispherical winter, from October until February. Besides the lake show a seasonal fluctuation in water level according to the seasonality of rains. Zooplankton was composed of at least 13 species, four Cladocerans, three Copepods, four Rotifers and other groups such as an Ostracod and the larvae of Chaoborus. The most abundant were Thermocyclops sp., Daphnia sp. and Keratella tropica. Their abundance fluctuated along the year, probably in response to changes in lake level and changes in hydrological conditions, increasing during dry season when the main outlet of the lake dried up. Changes in phytoplankton composition do not seem to be as relevant for zooplankton variation in this small lake.