Surfactant is pollutants that enter in to water ecosystem through industrial and urban sewages. The objective of this project is to determine the level of LAS and seasonal trend in eight different station of the Anzali wetland and compare them with maximum allowable value. In the study 96 samples of water were extracted by liquid–liquid method and the LAS were determined as methylene blue active substances (MBAS).The concentration of surfactant in the Pirbazar and the Caspian Sea stations varied from 0.176 to 0.422, and 0.098 to 0.049 mg/l while the seasonal concentration varied from 0.49 to 0.422 mg/l. The significant different were observed solely in the eastern of the Anzali wetland at the Pirbazar station (P < 0.05). The results showed that the highest of surfactant level measured about 0.27±0.10 mg/l at the Pirbazar station and the lowest recorded with 0.066 ± 0.022 mg/l in the Caspian Sea. The seasonal variations displayed, surfactant concentrations varied between 0.17 ± 0.07 and 0.10 ± 0.06 mg/l in winter and spring respectively, and average of 0.137± 0.037 mg/l. By the way no significant different were detected between seasons. In spite of this, LAS amount in water with other chemical material can create unfavorite effect on this ecosystem.