The objective of the research aimes to estimate the optimum amount of output to produce from vegetables grown under plastic houses. The vegetables include tomatoes, green beans, cucumber, hot pepper, and sweet pepper in the Jordan Valley regions, However, cost function analysis was used in this research, average variable cost and marginal cost are derived from total cost function for each crop in each region. The optimum amount of out put to produce can be determined by equating marginal cost with price of product. The break even can be estimate by equating the price of product with the minimum average variable cost.