The main objective of the research was studying the Economics of the Fully Mature Onion Production. A stratified random sample was drawn from 200 Onion Fully Mature growers in El-Gharbia Governorate were collected by personal interview, and secondary data secured from different sources during the study period (2000 – 2020). Descriptive and quantitative analysis were employed in data analysis to achieve study aims. The results of the research showed that:
1-     Areas planted, feddan productivity and production of fully mature onions at the national level and in El-Gharbia Governorate have been increasing, with statistically significant rates.
2-      The most important determinants of supply response at the national level were the farm price of a ton of winter onions in the previous year, but the area planted with winter onions in the previous year was the most important determinant of supply response in El-Gharbia Governorate.
3-     The production function for fully mature onions (Feddan and less) include four variables of labor, phosphate fertilizer, Number of seedlings, And the value of pesticides.
4-     The production function for fully mature onions (more than feddan) include three variables of labor, phosphate fertilizer and Number of seedlings.
5-     The optimum production, and profit maximization production were about 331.55 and 338.38 quintal respectively