Malaria is a worldwide public health problem, in 2017, and an estimated 237 million cases of malaria occurred worldwide compared with 211 million cases in 2010 and 219 million cases in 2015. Several countries used Indoor Residual Spray (IRS) (Bendiocarb 80%) to combat Malaria. The study aimed to evaluate the efficacy of IRS (Bendiocarb 80%) applied in Sennar state, Sudan in which Malaria is endemic. We used Pyrethrum spray collection, Bio efficacy of IRS using Cone methods and Malaria cases reporting to evaluate the efficacy of Indoor Residual Spray. The efficacy of IRS was tested by cone bioassay for four months (August- November 2017) for susceptible strains of Anopheles Mosquitoes. The recorded mortality of the 4 months was 99±1.23, 95±5.14,48±18.37, 23±9.26 respectively and mortality for the field strain of Anopheles mosquito in the study period was 100±0.0; 88.5±7.4; 43.8±20.1; and 0.7±0.8 respectively. The Malaria incidence rates for four months after application of Indoor Residual Spray in Sennar State (September, October, November and December 2017) were (5.18±3.4; 5.0±3.3; 4.31±3.1; and 5.15±3.9 respectively). This study found that there was a reduction in the total number of the collected Anopheles gambiae, female mosquito from 143 to 46, in unfed mosquitoes (UF) from 22 to 0, in fresh feed mosquitoes (FF) from 60 to18, in half gravid mosquitoes (HG) from 0.29 to 18, in gravid mosquitoes (G) from 32 to16, in density/room from 4.1 to 1.3, and in Man Biting Rate (MBR) from 2.5 to 0.7.Data analysed using statistical package for social sciences, version (22), Chi- square test used for the analysis of comparison, probability value of less than 0.05 considered statistically significant. The study concluded that there was a reduction in (Anopheles gambiae) density and Malaria cases after Indoor Residual Spray application in Sennar state, Sudan.