Increasing crop productivity through crop diversification under the same unit area has been considered as a way for sustainable intensification of cropping systems. This research was conducted on loamy sand soil at the Crop Research Station of Royal University of Agriculture (RUA) in Cambodia. The objective was to evaluate the growth and yield of maize (Zea mays L.) and mungbean (Vigna radiata L.) crops and land-equivalent ratio (LER) of maize-mungbean intercropping system using different seed rates of mungbean at 0% (0 kg ha−1), 25% (10 kg ha−1), 50% (20 kg ha−1), 75% (30 kg ha−1), 100% (40 kg ha−1) of recommended rates. The experiment was laid out using Randomized Complete Block Design (RCBD) with three replications. The agronomic traits and yield of both crops were measured at harvest. The weeds were removed three times to measure biomass. The results showed that there was no significant difference in agronomic traits and yield of maize under either maize-mungbean intercropping or maize monocropping irrespective of different mungbean seed rates. The highest mungbean seed rates as recommended did not decrease the growth and yield of intercropped maize. In contrast, the presence of mungbean in the intercropping suppressed weed growth significantly and the trend of weed biomass decreased with increasing mungbean seed rates. The intercropped mungbean grain yield decreased in comparison with monocropping mungbean. Overall, the land equivalent ratio (LER) was higher than 1 under the intercropping, showing its agronomic benefits, compared to monocropping. Therefore, maize-mungbean intercropping is a potential practice for improving productivity and managing weeds. Further research needs to be investigated under different ecological and social-economical niches to determine overall potential benefits and opportunities for scaling.