The availability of mosquito vectors is an important epidemiological factor in the transmission of mosquito borne diseases. The abundance of man-biting mosquito species was studied before and after indoor residual spraying (IRS) in three communities in Awka North and South Local Government Areas, Anambra State, Nigeria, between April and December 2013. Indoor biting and resting adult mosquitoes were collected using pyrethrum knockdown collection (PKC) method. Outdoor biting adults were collected using human bait collection (HBC) method. Larvae were collected by scooping. Chi square x², ANOVA and Simpson’s diversity index were used for data analysis. A total of 12,948 mosquitoes were collected. Larval collection was highest 9,871 (76.24%), indoor biting adults were 2,552 (19.71%) while the least was outdoor biting adults 525 (4.05%). The pre-residual spray collection of the mosquitoes 8,507 (65.70%) was almost twice higher than the post-residual spraying collections 4,441 (34.30%), and there was a significant difference (p = 0.000, p < 0.05). Mosquito species collected were Culex quinquefasciatus 1,437 (46.70%), Anopheles gambiae 1054 (34.25%), An. funestus 61 (1.98%), Aedes albopictus 257 (8.35%), Ae. aegypti 250 (8.12%) and Ae. bromeliae 18 (0.58%). Culex quinquefasciatus was the most abundant. The Simpson’s index of mosquitos’ diversity was higher during post-IRS (0.779) than pre-IRS (0.614). Indoor residual spraying was found to be a very effective mosquito vector control strategy. Occasional implementation of IRS and engagement of communities by government is recommended for efficient vector control.