Policy makers aim at promoting sustainable economic growth by keeping population growth rate low but there has been a substantial debate on whether population promotes, harms or has no effect on economic growth. Motivated by the divergent views, this study aimed at examining the effects of population change in Kenya on GDP. Using Time-series data for the period 1963 - 2013, this research examined the co-integration relationship between GDP growth rates and total population, unit root was tested using Augmented Dickey-Fuller, Co-integration test using Johansen’s Multivariate test and Granger causality test conducted to show the causality between the variables. The findings showed that for a unit increase in total population, there is rise of 2.221% in GDP. Its recommended that the Government needs to further promote investment level so as to increase job opportunities to utilize the population of the country.