To reduce malaria-related morbidity and mortality in Côte d’Ivoire, the National Malaria Control Program selected Indoor Residual Spraying as a complementary strategy to long-lasting insecticide-treated nets widely distributed in the country. As such, the current study was conducted to collect baseline information before IRS from May 2019 to August 2020 and to evaluate its effect on entomological parameters of malaria transmission from September 2020 to August 2021 after the intervention in Nassian, a high malaria endemic district of Côte d’Ivoire. Vectors were identified both morphologically and molecularly. the parity rate and the presence of Plasmodium falciparum sporozoite was determined. A total of 7,401 females of Anopheles were collected, of which 73.4 % before IRS and 26.6 % after IRS. Anopheles gambiae s.s. (85.2 %), An. funestus s.l. (14.2 %), An. nili (0.3%) and of An. pharoensis (0.3%) were collected. In baseline, the mean biting rate of Anopheles gambiae s.s was 17.5 bites/person/night. The mean parity rate was 81.5% with an average entomological inoculation rate of 1.2 infective bites/person/night. However, after IRS implementation, these parameters decreased respectivelly to 6.1 bites/person/night, the parity rate to 69.3 % and the EIR to 0.2 infective bites /person/night. A significant decrease of all entomological parameters was observed after the implementation of the IRS showing the positive effect of IRS on the vectors. However, following monitoring should be required including an epidemiological assessment to support the impact that was observed. This will guide the National Malaria Control Programme for future decision making and advocacy.