Abstract: This study was aimed at the determination of the relationships between the global solar radiation, relative humidity and mean air temperature of Ikeja, Lagos state Nigeria, for the month of June, 2016. The data of minimum and maximum temperature as well as the relative humidity and Microsoft excel tool was used for this work. From the study, it was observed that global solar radiation is affected by both the mean air temperature and relative humidity. The positive correlation of 0.460648 (46.648%) shows that global solar radiation increases with increase in mean air temperature. While global solar radiation increases with decrease in relative humidity based on its negative correlation value of -0.47686 (-47.686%). An accurate knowledge of solar radiation distribution at a particular location is very useful in the sizing of the thermal solar systems to estimates their performances.