Royal jelly (RJ) is known to possess several physiological and pharmacological properties. A dipeptide YY derived from RJ proteins is known to inhibit angiotensin converting enzyme (ACE) activity. Our previous study showed that the dipeptide YY inhibited the human renin activity at physiological pH. In this study, we investigated the pH dependency of the inhibitory effect of the dipeptide YY to the renin reaction with angiotensinogen. The renin activity was expressed at a wide pH range with two peaks around at 6.0 and 8.0. The dipeptide YY was found to inhibit the renin activity only at the acidic pH range lower than 8.0. The Ki was estimated 4.6 micromol/L at pH 6.0 when the Km of human renin was determined 0.07 micromol/L using sheep angiotensinogen as the substrate. The Km was 0.25 micromol/L at pH 8.5. A stereo structure of the complex of human renin with the dipeptide YY was modeled to discuss its non inhibitory effect on the renin activity at the basic pH. It possibly owes to a local sift of YY space from the center of renin cleft into the N-domain side of renin molecule at basic pH range higher than 8.0.