Allicin (AL) regulates the cellular redox, proliferation, viability, and cell cycle of different cells against extracellular-derived stress. This study was to investigate the effect of allicin treatment during in vitro maturation (IVM) on porcine oocyte maturation and developmental competence. Porcine follicular oocytes were cultured in 0 (control), 0.01, 0.1, 1, 10, and 100 μM AL added IVM media. The rate of polar body emission was higher in the 0.1 μM AL-treated group (74.5% ± 2.3%) than in the control (68.0% ± 2.6%). After parthenogenetic activation, the rates of cleavage and blastocyst formation were significantly higher in the 0.1 μM AL-treated group than in the control (p < 0.05). The reactive oxygen species level at metaphase II was not significantly different among all groups. In matured oocytes, the relative mRNA expression of both BAK and CASP3, and BIRC5 were significantly lower and higher, respectively, in the 0.1 AL-treated group than in the control. Also, the mRNA expression of BMP15 and cyclin B, and the activity of phospho-p44/42 MAPK, was significantly increased. These results indicate that supplementation of oocyte maturation medium with allicin during IVM improves the maturation of oocytes and the subsequent developmental competence of porcine oocytes.