This study aimed to determine the effect of tea planting age on stoichiometric ratios of microbial biomass carbon (MBC), nitrogen (MBN), and phosphorus (MBP) and soil microbial quotient (SMQ, expressed as qMBC, qMBN, and qMBP, respectively). A chronological sequence of tea plantations (3, 8, 17, 25, and 34 years) was selected in a small watershed in the Three Gorges Reservoir Area, and a slope farmland was selected as control. The results showed that with the increase of tea plantation age, soil and microbial biomass C, N, P contents, soil C:N and C:P elevated significantly, while soil N:P overall declined; the MBC:P and MBN:P increased first and then decreased, but MBC:N varied insignificantly. The tea plantation age affected SMQ notably. qMBC first decreased and then increased following the tea planting age, while qMBN and qMBP went up in a fluctuating pattern. In this study, qMBC positively correlated with soil N:P and microbial biomass C:N:P, but negatively correlated with soil C:N and C:P; on the contrary, qMBN and qMBP negatively correlated with soil N:P and microbial biomass C:N:P, but positively correlated with soil C:N and C:P. Generally, the variations of soil microbial biomass and SMQ could reflect the soil quality of tea plantations.