Due to the slow growth and long gestation period of oil palm farmers are often faced with challenges of weed control before oil palm canopy closure hence the need to introduce plantain as component crop with the oil palm. A two years trial was conducted in in Ovia North East LGA, Edo State, Nigeria (Latitude 6.636oN, 6.909oN and Longitude 6.182oE, 6.364oE) to evaluate the effect of NPKMg fertilizer and interplanted cassava on growth and yield of plantain in oil palm based system. The treatment consisted of NPKMg fertilizer as the main block treatment (with and without NPKMg fertilizer) and crop combinations [oil palm/plantain (OPP) and oil palm/plantain/cassava (OPPC)] as sub block treatments. The treatments were laid out in split block arrangement in RCBD replicated thrice. Data were collected on plantain plant height, number of leaves/pseudostem, leaf area index, number of suckers/pseudostem, number of days to 50% flowering of main psuedostem and first ratoon plants, number of days to first appearance of peeper sucker from main pseudostem, number of leaves at flowering from main pseudostem and first ratoon plants, finger weight (kg/bunch), finger circumference/finger (cm), finger length/finger (cm), number of fingers/bunch, biomass weight (t/ha), number of bunches/ha and bunch yield (t/ha). NPKMg fertilizer significantly increased (p<0.05) the growth and number of sucker produced. Plantain planted in OPP combination had taller plant and more number of suckers (first ratoon plant and second ratoon plant, respectively) relative to those in OPPC combination while plantain planted in OPPC combination lead to delayed appearance of peeper suckers, delayed fruiting of plantain and resulted to 18, 15.8, 1.6, 6, 8.3 and 12 % increase (p<0.05) in plantain bunch weight, finger weight, finger circumference, finger length, number of fingers and biomass weight, respectively relative to those in oil palm/plantain (OPP) combination.