Cotton picking in Egypt is a major problem, where he still picking by hand it represents a large molecule of the production costs, so The present work is an attempt to design a machine to mechanization the process of Egyptian cotton picking to overcome the conditions of Egyptian agriculture, and the obstacles of physiological of Egyptian cotton varieties and farming methods. Toovercomeall theseobstacles, and was bought to satisfy the need to develop and use new and important agricultural machinery technology. The aim of the present study was to develop, manufactured and quantifies the performance of a self-propelled mechanical cotton harvester. This harvester has main construction advantages., Firstly it is a self-propelled, it can control high , , it can control distance between rows and low damaged steams of plant. The developed cotton harvester was fabricated under the supervision of Agricultural.Engneer.Department, Mansoura University in private local workshops in Dekernes city, El_Dakahlia governorate and field tests at Ashmoon village. The performance effectiveness of the developed cotton harvester. Best results were obtained when using forward speed approaching to 0.36 m/s with a modified form of plant density the efficiency of picking about 70% at the machine performance rate almost 3.5 hours per faddan that when using 4 units for picking 2 rows at same time. Also getting less yield loss when using only two units to harvest a single row. Thus can access the best methods for mechanization the harvesting of Egyptian cotton. In other way can improve harvest efficiency from 70% to 97%, by re-picking three times or more.