Located near to the equator, Malaysia has a tropical climate that is warm and humid throughout the year. With average rainfall received all over Peninsular Malaysia of about 2500 mm per year, aged leachate constituents and its concentration is affected. This paper investigates the relationship between concentration of leachate constituents and rainfall received over study period. Results achieved by analysing parameters to compute leachate characterization and then coincide to rainfall received. Parameters identified to be critical for leachate characterization are Chemical Oxygen Demand (COD), Total Organic Carbon (TOC), Volatile Organic Carbon (VOA), Ammoniacal Nitrogen (NH<sub>4</sub>-N) and heavy metals; iron, copper and chromium. Results showed that rainfall has a significant effect to COD, TOC, NH<sub>4</sub>-N, and heavy metals where their concentration is greatly reduced to a much lower value with presence of rainfall. However, values of VOA are not affected by rainfall received over the period of study.