Yala River is one of the several rivers that drain into Lake Victoria in East Africa. Lake Victoria is the Worlds second largest freshwater lake and is the source of the Nile River. Rainfall and flow data for the period 1963-1998 were used for this study. The time series of monthly and annual values of rainfall and discharge were analyzed using statistical methods. Trend analysis was performed and the best-fitted models were determined using the statistical criteria of Mean Error (ME), Mean Square Error (MSE), Mean Absolute Error (MAE) and Mean Absolute Percent Error (MAPE). This was done in an attempt to determine whether or not there have been any significant changes in rainfall and discharge over this catchment. Probability distributions were fitted and the chi-square, Anderson-Darling and the Kolmogorov-Smirnov tests were used to select the theoretical distribution, which best fitted the data. The analogue years plots were also carried out in order to distinguish the years with near normal, above normal and below normal conditions, using the long term mean of the variables. While rainfall data analysis for the stations analyzed shows on average a decreasing trend, river discharge shows a decreasing slope in the upstream station and an increasing trend in the downstream station.