This study was carried out in the northern part of the Bay of Iskenderun in the northeastern Mediterranean during the period 1994-1995. The quantitative and qualitative distribution of phytoplankton, the environmental factors that affect its distribution and the changes in succession over time were investigated. At each of the seven stations, monthly sampling was done from the surface and 10.0 m depth. In spring, the sampling was performed once every two weeks. In addition, the measurements of some physical and chemical parameters i.e. temperature, salinity, ($NO^{-}_3$ +$NO^{-}_2$ )-N and $PO4^{-}_3$ -P were carried out. At the end of the study, a total of 170 taxa from 5 algae classes, Cyanophyceae, Dinophyceae, Prymnesiophyceae Dictyochophyceae and Bacillariophyceae were determined. Bacillariophyceae was found to be richer than the other groups in terms of abundance and species number and followed by Dinophyceae. Cyanophyceae, Prymnesiophyceae and Dictyochophyceae were represented by only one species each.