Abstract: An analysis of the amino acids present in the hemolymph of Culex pipiens pallens caught from resting or overwintering places (blood meal: Sella 1, i.e. empty; ovary stage: under Christophers IIb) in Zhengzhou (34°43'N,113°39E) indicated that 19,18 and 18 kinds of free amino acids (FAAs) were detected during stages of preoverwintering,overwintering and pos-toverwintering respectively. Comparison of hemolymph amino acids between overwintering and preoverwintering stages revealed that the concentrations of the total FAAs and FAAs reduced significantly in overwintering except cystine and proline. The concentrations of cystine and proline during preoverwintering were 0. 1563 ±0. 0021 nmol/μl and 22. 2467 ±1. 3537 nmol/μl, but 0. 2067±0. 0058 nmol/μl and 36. 5467 ±0. 4654 nmol//μl during overwintering respectively. Comparison of hemolymph amino acids between postoverwintering and overwintering stages showed that the concentrations of all FAAs and total FAAs increased significantly during postoverwintering stage, and the concentrations of aspartic acid, glumatic acid, alanine,cystine, proline and total FAAs even exceeded those during preoverwintering stage respectively.