Mangoes are a popular home garden crop in Brunei Darussalam, and their leaf litter is often used as compost, which is an environmentally friendly approach to manage organic waste. This study was conducted in 2018 at Universiti Brunei Darussalam to investigate the allelopathic effects of mango leaves on the growth of a leafy vegetable, Pak choi. Powdered and aqueous extract of mango leaves at various mango leaf concentrations (0-30%) were prepared and mixed with potted soils. Seedling survival, number of leaves and relative growth rates (based on stem diameter and shoot height) of Pak choi was not significantly affected by mango leaf treatment types and concentrations. Irrespective of mango leaf treatment types (powder vs. aqueous extract), biomass allocations to leaves (LMR) and roots (RMR), but not stems (SMR), were significantly inhibited at 10% and 20% mango leaf concentrations, respectively. However, stimulation in LMR and RMR of Pak choi was significantly observed in the opposite mango leaf concentrations. The aqueous mango leaf extract significantly stimulated specific leaf area (SLA) of Pak choi, suggesting that it probably contain less potent allelochemicals compared to the leaf powder, which inhibited SLA by almost 100%. Number of leaves and relative growth rates of Pak choi were not significantly affected by mango leaves. The findings suggest that aqueous mango leaf extracts at 20% could possibly be used in a sustainable organic leafy vegetable farming due to its growth stimulation in LMR and SLA. However, further research on other leafy vegetables and in field conditions are necessary due to the inhibitory allelopathic potentials of mango leaves.