Product efficiency of irrigation lowland organic paddy farming system research had been conducted in November – December 2015 at Barokah Farmer’s Group in Semarang Region. Purposive sampling was used to choose location based on Organic Agro Ecological Zone. This research aimed to analyze farmer’s rationality in using production factor. Multiple regression linear was used to analysis the factors influencing production and was continued by allocate efficiency test. The result showed that organic paddy farm was profitable and farm scale, seed, manure, labor and irrigation have positive effect and significant on production factors. Then, to find maximum benefit, farmer needed reduce the use of seed, fertilizer and labor. Therefore, to reach both optimum production and advantage need to extend planting area.