Abstract: Effect of turbidity on the fluorescence intensity determination of chlorophyll-a in water was studied. Spectrofluorophotometer was used to measure the the fluorescence intensity of the solution microcystis aeruginosa and the extract of chlorophylla with different turbidity. The concentration of chlorophyll-a in microcystis aeruginosa and water samples with different turbidity was determined using the on-line detector for chlorophyll in seawater. It was found that the measured concentration of chlorophyll-a was high due to the strong scattering effect of suspended particules when water turbidity was high. The effect of turbidity was negligble when the water was transparent.