Rainfall variability, seasonality and extremity have a lot of consequences in planning and decision making of every spheres of human endeavour especially in Nigeria where majority of agricultural practices and planning is dependent on rainfed agriculture. This project considered the trend and seasonality of rainfall in South-Western Nigeria. We employed the non-seasonal and seaonal unit root tests of Dickey and Fuller (1979) and Helleberg, Engle, Granger and Yoo (1990) respectively. Both tests confirmed the seasonality of rainfall in the six states of the geo-political zone. As a result, Seasonal ARMA (SARMA) models were therefore proposed in predicting rainfall pattern in the states.