Abstract: A greenhouse study was carried out to investigate the effect of moisture on the growth and thymol and carvacrol contents of Mexican oregano (Lippia berlandieri) under controlled conditions. There were 4 watering schemes (0.2, 0.4, 0.8 and 1.2 l water per pot per 15 days) and 3 growth phases, i.e. seedling (30 days after transplant (DAT)), full flowering (60 DAT) and maturity (90 DAT). The crop yield increased significantly with increasing moisture and age of the plant. Although on an average, the older plants contained less oil than the younger plants, the differences were not statistically significant. The total thymol and carvacrol contents of oregano oils obtained from younger plants were higher than that of the mature plants. The amount of water received by the plants did not have a significant effect on the thymol and carvacrol contents of the oil.