Summer crops and vegetable production, in addition to increase employment and agricultural products, develop land productivity. The aim of this paper is to evaluate the cost and benefit of summer crops and vegetables production in Iran during 2006-07 using Lanjan's greenhouse farmlands as a case study. The method of the study is cost-benefit analysis. The findings of the research showed a positive net present value an capital recovery, specially in traditional farmlands in short term. The benefit-cost ratio was greater than one and internal rate of return was greater than acceptable interest rate. The results also showed that except in one case, benefit- cost ratio is greater than unit indicating profitability of investment in greenhouses. The sensitivity analysis showed that the profitability is highly sensitive to cost production. Crop rotation was found to be an essential practice in the way that growing summer crops is preceded by vegetable production.