In the study carried out to determine the effects of light intensity, temperature, nitrogen defi-ciency and aeration on the vegetative growth and form of the cysts of the green alga Haemato-coccus pluvialis in the laboratory conditions, vegetative growth of the cultures were found similar at the light intensities of 27 and 48 μmol photon m-2s-1 and % 2-10 inoculation amounts. H. pluvialis cultures were exposed to the 177 and 379 μmol photon m-2s-1 light inten-sities and N-deficient condition to form cyst and accumulate astaxanthin. While 27 and 48 μmol photon m-2s-1 light intensities caused the accumulation of astaxanthin at the low cell con-centrations, 177 μmol photon m-2s-1 irradiance was insufficient to turn red the cells in the nitro-gen-deficient medium and high cell densities. The highest astaxanthin content of % 3.605 was obtained from the cultures aerated, at the irradiance of 379 μmol photonm-2s-1 and 24°C. In the study, it was observed that 35°C temperature and 177 μmol photon m-2s-1 irradiance caused the death of the cells.