Oil palm (Elaeis guineensis) is one of Indonesia’s important oil-based plantation crops. The problem with oil palm planting is the long duration from initial planting to harvesting of the fresh fruit bunches. A possible solution to improve farmers’ income is to plant oil palm in an intercropping system. This research compared the monocropping and intercropping systems in the immature oil palm stage. This study aimed to evaluate the growth performance of oil palm in an intercropping system with maize using the Sustainability Index (SI) model. The experiment was conducted at the Ciparanje Experimental Field, Universitas Padjadjaran, Indonesia in February-May 2019, 2020 and 2021. In terms of treatment, a monocropping system and an intercropping system of oil palm with maize were replicated four times. The observation variables were plant height, frond number, stem diameter, leaf chlorophyll index, and stomatal conductance. The SI analysis was calculated to observe plant growth consistency. The evaluation results showed no significant effect on the growth performance of immature oil palms through monocropping and intercropping over three years. The SI value showed the variation level in the sustainability of immature oil palm. The majority of SI showed a moderate category, which led to the conclusion that immature oil palm in various cropping systems was stable for the first three years. The intercropping system with oil palm and maize showed similar result to the monocropping system in the three years of the immature oil palm phase.