Miankaleh international wetland and peninsula are one of the main UNESCO biosphere reserve in Iran and Middle East. Phytoplankton diversity of the Miankaleh wetland was investigated from October 2009 to September 2010. Apart from the work done by Ramezannejad Ghadi, this study is the second floristic study of algae in the Miankaleh wetland in north of Iran. Five main algal groups were recorded namely: Bacillariophyta, Cyanobacteria, Chlorophyta, Euglenophyta and Xantophyta. A total of 94 species and varieties belonging to 47 genera were identified. Among them green algae formed the most abundant group making up 43 species and varieties from 18 genera. This was followed by Diatoms, with 31 species from 15 genera, Cyanobacteria, with 18 species from 12 genera. Euglenophyta and Xantophyta with 1 species make up an insignificant part of taxa. All of these taxa are new records for Miankaleh wetland and Mazandaran province.