Abstract: Primary productivity , biomass and chlorophyll2a of size fractionated phytoplankton ( < 0. 2μm, <2μm and < 200 μm) were estimated in three ponds. The ratio of the concentrations of chlorophyll2a of the phytoplankton to the total chlorophyll2a in the corresponding size of pico2 (<2μm) , nano2 (2220μm) and micro2 (202200μm) in the experimental ponds 14 was 3. 7 % , 82. 9 % and 13. 4 % , respectively. The ratio of the production of size fractionated phytoplankton to the total phytoplankton production corresponding to pico2, nano2 and micro2algae were 13. 6 % , 66 % and 20. 4 % , respectively. The ratio of the concentrations of chlorophyll2a of the phytoplankton to the total chlorophyll2a in the corresponding size of pico2 (<2μm) , nano2 (2-20μm) and micro2 (20 -200μm) in the experimental ponds 11 was 4. 5 % , 16. 1 % and 79. 4 % , respectively. The ratio of the production of size fractionated phytoplankton to the total phytoplankton production corresponding to pico2,nano2 and micro2 algae was 9. 0 % , 78. 9 % and 12. 1 % , respectively. The ratio of the concentrations of chlorophyll2a of the phytoplankton to the total chlorophyll2a in the corresponding size of pico2, nano2and micro2 algae in the experimental ponds 15 was 4. 7 % , 22. 3 % and 73. 0 % , respectively. The ratio of the production of size fractionated phytoplankton to the total phytoplankton production corresponding to pico2, nano2 and micro2 algae was 12. 4 % , 60. 8 % and 27. 8 % , respectively. Nano2algae are important producers in rotifer culturing ponds ecosystems.