The bitter gourd is bringing health benefits to human; however bitterness of the fruit limits its therapeutic effects. Fermentation processes have been reported to be able to reduce the bitterness of the bitter gourd. In this study, effects of fermentation factors including time (0, 12, 24, 36, 48, 60 and 72h), temperature (20, 25, 30, 35 and 40℃) and inoculum volume (v/w) (0, 1, 5, 10, 15 and 20%) of Lactobacillus plantarum on pH, total soluble solids (TSS), total phenolic content (TPC), antioxidant capacity (AC) and bitterness evaluation of the bitter gourd juice were studied. In general, TPC and AC values of the fermented samples increased significantly (p < 0.05) compared to those of the control ones. In the first experiment, the TPC value of 24h-fermented sample reached a peak, meanwhile the highest AC value obtained after 72h fermentation. In the second experiment, the highest TPC and AC values were recorded at 40℃. For the last experiment, with 20% inoculum volume, the highest TPC and AC values were recorded. The fermentation with 10% of L. plantarum for 24 h, at 30℃ resulted in a higher total phenolic content. Changing fermentation conditions significantly changed bitterness of the juice. Through sensory evaluation test, significant differences (p<0.05) in the bitterness among unfermented and fermented samples were recorded. Most of the panelists recognized there was reduction in bitterness of fermented sample compared to the control one.