Sweet potato is grown across a wide range of agro ecological zones. In Nigeria, tuber yields differ considerably across agro ecological zones and even from farmer to farmer. This wide variation in tuber yields is a matter of concern because it means that the total output of the crop is lower than it should be. This variation could be as a result of factors such as inadequate supply of water from either rainfall or irrigation, temperature and humidity level of the location, soil fertility, relative humidity and varieties of the sweet potato plant. In order to better understand the variations in sweet potato tuber yield in different locations and seasons, results from 10 sweet potato varieties from four different environments over two years were examined. Field experiments were conducted at the same time in four locations (Igbon via Ejigbo (Osun State), Ibadan (Oyo State), Idofian and Ilorin (Kwara State) for two growing seasons in 2015 and 2016. Ejigbo (Osun State) and Ibadan (Oyo State) belong to the rainforest zone while Idofian and Ilorin (Kwara State) belong to southern guinea savannah. Rainfall data for the period of the experiment were obtained from the metrological stations in these areas. At four weeks after planting data was taken on dead plants. Also, at harvest data on the yields of the sweet potato from the four locations were collected and subjected to statistical analysis. The estimation of field condition assessment was good for Ibadan and Igbon due to high amount of rainfall in the area. Also, the sweet potato tuber yield was consistently higher for all the varieties in this rainfall zone; however, the situation is contrary in Ilorin and Idofian. As a result, rainfall variability (rainfall amount) was identified as a factor that could lead to missing stands (plant that failed to germinate and could not survive after planting) and poor yield. It is recommended that care should be taken by sweet potato growers to address the factor so as to increase productivity of their sweet potato production.