Background: Mosquitoes are the most important blood feeding insects that can transmit serious diseases such as malaria and arboviruses. Each species of mosquitoes selects a specific host according to biological conditions of the region and genetic characteristics. Anopheles maculipennis complex and Culex theileri are dominant mosquito species in Zanjan. This study was carried out in order to determine the blood feeding index of mosquitoes by Sanduwich Enzyme Linked Immunosorbent Assay (ELISA) in 2004. Materials and Methods: An. maculipennis complex and Cx. theileri mosquitoes were collected from indoors and outdoors by pyrethrum spray catch (PSC) and light trap in 2003 and blood fed samples were separated and kept at -20°c subsequent to drying. The samples were tested for human blood after establishing Sandwich ELISA technique. The results were analyzed through test. Results: A total of 6436 samples were studied, out of which 3072 (47.73%) were An. maculipennis and 3364 (52.3%) Cx. theileri. Human blood-feeding index in An. maculipennis complex was 3.2% while this rate reached 1.5% in Cx. theileri. An. maculipennis complex showed 2.12% more anthropophilic behavior than Cx. theileri. Anthropophilic index of this anopheles by PSC was 0.2%. This index was 7.3% (93) in samples collected by light trap. There was a significant difference in two rates (p=0001). In PSC samples anthropophilic index was 35.17 times less than light trap samples. Anthropophilic index of this Culex was 1.8% through PSC and 1.3% through light trap, which shows no significant difference. Conclusion: With regard to high human blood feeding index of An. maculipennis complex, we suggest that health officials of the province pay careful attention to malaria control and monitoring programs. To reduce human blood feeding index people should be encouraged to use personal protection and keep livestock to divert mosquitoes. More research associated with molecular biology, ecology and bionomy is recommended to determine this difference.