Forage corn is a plant with short growing period that can be used for livestock feeding and can indirectly be used in producing meat and its byproducts in human food. It can be used as forage or silage in livestock feed. Forage corn is grown in the crop production unit with different size in Isfahan township. crop production unit size is one of the factor that can affect forage corn production productivity. The Purpose of this research is to determine the effect of production unit size on forage corn productivity in central county of Isfahan township. In this research, a random stratified sample of 101 forage corn farmers was used. Data was collected through interveiws with farmers and filling out questionnaires. Data included those related to incomes, inputs (land, seed, fertilizer, pesticide, machinary, and labor), and personal characteristics of farmes (such as age, gender, experience and education level). For analysis, a log-log regression model was used. The regressions were estimated in two stages. In the first stage, production elasticities were estimated. Using these elasticities and the actual values for inputs and output for each farm, total factor productivity(TFP) were culculated. The culculated TFPs were regressed against the independent variables. The results showed that farm size, pesticides, phosphate fertilizer and primary level of education had positive and statistically significant effect on forage corn production productivity. Nitrogen fertilizer and number of farm plots had negative effect, however.