Oil palm (Elaeis guineensis Jacq.) is a significant commodity in Indonesia, but its productivity, especially in smallholder plantations, is still relatively low. This study aims to evaluate the effect of a combination of compound NPK fertilizer and biological fertilizer on soil nutrient availability, soil microbial activity, and growth and productivity of eleven-year-old oil palm. The study used a factorial randomized complete block design (RAKL) with four doses of compound NPK (0, 3.1, 6.2, 9.3 kg/tree/year) and four doses of biological fertilizer (0, 0.25, 0.5, 1 kg/tree/year), each repeated three times. The results showed that high doses of compound NPK (M3) and biological fertilizer (H3) significantly increased the number and weight of fresh fruit bunches (up to 1.86 bunches/tree/month and 25.8 kg/bunch), as well as annual productivity (up to 29.4 tons/ha/year). Soil N, P, and K content and beneficial microbial populations such as Azospirillum, Aspergillus, and Azotobacter increased sharply after treatment. The ratio of female to male flowers responded positively to rainfall and was more stable in the biofertilizer treatment, indicating better physiological resistance to environmental stress. The integrated use of compound NPK and biofertilizers has been shown to increase nutrient absorption efficiency, improve soil biological health, and support sustainable oil palm production.