The current study attempted to investigate the economic issues of Barely crops in Tehran Province of Iran. The data were collected in association with Tehran province Agricultural – Jahad Organization. Two-stage stratified random sampling method used to select samples and sample size is about 250 farms. The Trans log and polynomial function was used to estimate cost functions. The results showed that, the optimum size of barley farms in the case of small and medium, large and total farms groups were 17.08, 41.96 and 46.43 ha, respectively. It was greater than the average sample farm size in the case of small and medium farms group (2.96 ha) and total farms group (18.21 ha). The average total cost decreases with increase in farm size and reaches its minimum when area is 17.08, 41.96 and 46.43 ha in small, medium, large and pooled sample farmers groups, respectively. Beyond these levels of area, the average total cost increases at increasing rate. The estimated optimum size of farms showed the fact that the most profitable farm size for all farm size groups belongs to large category of farms.

Key words: Cost function, optimum size, Tehran province, barely crop, Trans log cost function.