The purpose of this paper is to clarify the economic efficiency of marginal manual labor input on mandarin orange production with econometric methods. For this purpose, two points are investigated. First is to estimate the marginal revenue product of manual labor input. Second is to compare estimated marginal revenue product with its cost, that is the wage rate of manual labor. The main conclusions of this paper are summarized as follows: (1) In growing period, manual labor is the most influential in profit of all inputs. Moreover, in harvesting period, labor is the most influential. These results suggest that mandarin orange production have labor-using technological feature. (2) Judgingg from equilibrium condition I, which means that the relative marginal revenue products of all inputs must be equal to those inputs' relative prices, manual labor input is shorter than another inputs in most farms. (3) Marginal revenue product of manual labor input estimated by equilibrium condition II, which concerns the distribution of profit to inputs in each period, is lower than its cost in some farms. This result suggests that marginal manual labor input can not always increase profitability of all farms.