Cation exchangeable capacity (CEC) is a significant soil chemical property influencing the availability and exchange of cation nutrients in soils. This study aims to quantify the alterations in CEC of reclaimed mining soil (RMS) treated with oil palm bunches (OPB) and coal fly ash (CFA). The experiment was carried out by adding 3 levels of OPB (0, 20, and 40 Mg ha−1) and CFA (0, 50, and 100 Mg ha−1) were counted to RMS. After 15 days of incubation, CEC with other soil chemical characteristics were measured. The results indicated that the application of 40 Mg ha−1 of OPB increased soil CEC from 20.4 cmol kg−1 to 35.6 cmol kg−1, and 100 Mg ha−1 of CFA caused a 25% decrease. These changes in CEC were associated to the fluctuation in number of functional groups due to the addition of OPB and CFA. The results suggested that adding organic matter could initiate a decrease in CEC due to the presence of multivalent cations from ash, thereby increasing net soil CEC.