The importance of picoplankton in calcite precipitation has increasingly received attention in recent years. There is some evidence supporting calcite precipitation by picoplankton but the mechanisms elicited in the process are still far from clear. This study investigated the role of picocyanobacterial photosynthesis in inducing calcite precipitation. The precipitation of calcite was induced by addition of cyanobacterial cells Synechococcus strain PCC 7942 to solutions of CaC03 at different saturation states. Precipitation experiments were performed under controlled laboratory conditions in two set-ups: one in which photosynthesis was inhibited using a herbicide called Diuron and the other one in which photosynthesis was operational. Induction times for the two set-ups were compared. During the experiments, a pH meter monitored the pH and Ion Selective Electrodes monitored concentrations of CO32- and Ca2+. The morphology of the precipitated crystals was analysed by Scanning Electron Microscopy. Calcite precipitation occurred earlier in experiments in which photosynthesis was blocked inferring that picocyanobacterial photosynthesis does not play a major role in calcite precipitation. The microscopic observations provide some evidence that cell walls of Synechococcus strain PCC 7942 act as a template for calcite nucleation.