Vertical and temporal dynamics of Cryptophyceae population was studied in an oligo-mesotrophic reservoir, the Ninféias Pond, located in the Parque Estadual das Fontes do Ipiranga, south of the Municipality of São Paulo, state of São Paulo, southeast Brazil. Material studied was collected from January to December 2000. Individual specimens of Cryptophyceae were present in all samples. Thermal stratification and mixing processes do not seem to directly influence temporal distribution of Cryptophyceae, but may interfere in their vertical distribution. Four out of the 10 species presently identified (C. brasiliensis, C. curvata, C. erosa and C. marssonii) presented greatest population densities and highest frequency of occurrence. PCA showed that the species' vertical distribution scale was more important towards ordination of samples. Greatest growth of C. erosa was noticed below 1 m depth in all months sampled. Cryptomonas brasiliensis was highly representative at the surface of reservoir, mainly during the warmer months (January-February, October and November). Considering the temporal scale, results did not demonstrate seasonal distribution of Cryptophyceae, but in the vertical scale, results evidenced a heterogeneous distribution of the group.