Traditionally, it is believed that the substrate and products of a monoacylglycerol lipase (MGL) share the same path to enter and exit the catalytic site. Glycerol (a product of MGL), however, was recently hypothesized to be released through a different path. In order to improve the catalytic efficacy and thermo-stability of MGL, it is important to articulate the pathways of a MGL products releasing. In this study, with structure biological approaches, biochemical experiments, and in silico methods, we prove that glycerol is released from a different path in the catalytic site indeed. The fatty acid (another product of MGL) does share the same binding path with the substrate. This discovery paves a new road to design MGL inhibitors or optimize MGL catalytic efficacy.