The objectives of the study were to compare the content of nitrate in leafy vegetables when irrigated with inorganic fertilizers and biogas effluent. Three continuous crops of water spinach (Ipomoea aquatica) and leaf mustard (Brassica juncea L.) irrigated by biogas effluent (BI) and inorganic fertilizer (IF) in different treatment of (i) 100%BI, (ii) 75%BI+25%IF, (iii) 50%BI+50%IF, (iv) 25%BI+75%IF, (v) 100%IF and (vi) control treatment of 100% pond water (PW). For each crop, six treatments were arranged randomly on-field. The results showed that there was not significantly difference between the accumulation of nitrates in both water spinach and leaf mustard in each treatment, while the nitrate content in treatments using combined BI and IF was always lower than using 100%IF. The nitrate content of water spinach was lowest when irrigated by 100%BI (39.4 - 52.6 mg/kg fresh weight). The leaf mustard’s one was lowest if irrigated by 75%BI+25%IF (32.1 - 37.0 mg/kg fresh weight) of which were not significantly difference comparing with irrigated by 100%PW. In additional, the yield of water spinach and leaf mustard in treatments used BI increased gradually through the crops. In crop 3, the yield of water spinach was highest when irrigated by 100%BI (2.9 kg/m²), and leaf mustard yield was highest when irrigated 100%BI and 75%BI+25%IF (1.9 - 2.1 kg/m²), which were not different with irrigated by 100%IF. Apply biogas effluent to irrigated leafy vegetables could limited nitrate accumulate which cause safety to in the vegetables.