Basil (Ocimum basilicum L.) essential oil phenylpropenes have ecological and economic importance. These compounds are specifically synthesized and accumulate in basil peltate glandular trichomes, and their content and composition depend on plant developmental stage. Studies on gene expression and enzymatic activity indicate that the phenylpropene biosynthetic genes are developmentally regulated. These previous studies, however, did not systematically investigate the levels of gene expression, enzyme activity, and phenylpropene accumulation through plant development. In this study, we systematically investigated methylchavicol accumulation in basil leaves and the enzyme activities and gene expression of both chavicol O‐methyltransferase (CVOMT) and eugenol O‐methyltransferase (EOMT) in all leaves at four plant developmental stages. Methylchavicol accumulation decreased over time as the leaves matured. There was a significant correlation between methylchavicol accumulation and CVOMT and EOMT enzyme activiti...