We have previously reported that piperine, a known piperidine alkaloid from Piper longum, competitively inhibited mouse brain MAO-A and MAO-B activities. Piperine also showed in vivo antidepressant-like activity against the tail suspension test. In the present study, we further expanded on the identification of MAO inhibitors from the fruit of P. longum. Activity-guided fractionation of a methylene chloride soluble extract led to the isolation of three known piperine-related compounds, methylpiperate (1), guineensine (2), and piperlonguminine (3). Of these, methylpiperate (1) and guineensine (2) showed significant MAO inhibitory activities with $IC_{50}$ values of 3.6 and $139.2;{mu}M$, respectively. Furthermore, methylpiperate (1) exhibited a selective inhibitory effect against MAO-B ($IC_{50}$ value: $1.6;{mu}M$) than MAO-A ($IC_{50}$ value: $27.1;{mu}M$). The kinetic study using the Lineweaver-Burk plots analysis suggested that methylpiperate (1) competitively inhibits MAO-A and MAO-B activities with the Ki values of 23.5 and $1.3;{mu}M$, respectively.