Periphyton apply to Micro Organism consist of plants and animals of steady and plunging levels in water source. They are very important for marine's nutrition and they refine contaminant waters. In spite of its importance there is worthless research in Iran. This research accomplished as recognition of herbaceous Periphytons of Jajrood River and studying of environmental factors effects on their varieties through 6 months July to December 2004 in 5 stations between Latian and Mamlo dam. The sampling was natural and monthly from herbaceous Periphytons. And environmental factors like water air temperature PH Phosphate, Nitrate, total hardness, Alkalinity, solution Oxygen, Dioxid Carbon and speed of water were estimated. At final, from 4 algal branches Cyanophyta, hlorophycophyta Chrysophycophyta and Pyrrhophycophyta, 6 genuses of Periphytons were recognized. These results showed the most important effective environmental factors on Periphytons of Jajrood River contain water&air temperature, Nitrate, Alkalinity and total hardness. And other factors had not important effects.