Artocarpus altilis is known to be one of the plants having antifungal property and this study aimed to test its efficacy against Aspergillus niger causing black molds in onion. The study was laid out in complete randomized design composed of four treatments replicated thrice: T1 – control (inoculated with A. niger only); T2 – with 25% A. altilis leaf extract; T3 – 50% and; T4 – 75%. Appearance of symptoms 3 days after inoculation and zone of inhibition were observed and recorded. Results showed that there are no significant differences on the inhibition zone among the treatments and was considered as resistant to the antifungal activity of A. altilis since it exhibited a zone of inhibition which is less than 10 mm in diameter. However, in the observation of symptoms manifestation, those applied with 50% A. altilis leaft extract exhibited less symptoms in 51 days of observation but major shriveling happened in those applied with 75% A. altilis leaf extract which could indicate that the application of 50% A altilis extract is the optimum concentration to control black molds in onion. Knowledge on the efficacy of A. altilis extract against A. niger in onions would be useful in extending the shelf life of onions in the market and help prevent post-harvest losses.