Abstract: Under the laboratory condition, the larvae of Culex pipens fatigans may feed mainly on Anabaena sp and complete their life cycle. The retention time of Anabaena sp. in larval intestine is about 6 hours while that of Saccharomyces sp. is about 5 hours, meaning that Anabaena sp. is not so digestible for the larvae. From hatching to pupation, the larvae fed with Anabaena sp.lasted 194 hours and those fed with Saccharomyces sp were 142 hours, showing that the duration for completing larval stage of the former is 52 hours, which is longer than those fed on Saccharomyces.