An electrical connector includes an insulative housing composed of a plurality of parallel partitions each extending in a longitudinal direction, and plural rows of contact modules each extending in the longitudinal direction and disposed in the housing. Each contact module includes a plurality of contacts integrally formed within an insulator/wafter which extends in a longitudinal direction. In each contact module, each contact includes a main body with opposite contacting arms on upper and lower sections. The contact modules are successively assembled downwardly in the housing by plural assembling poles each of which retainably extends through plural contact modules in the transverse direction and retained in the corresponding positioning grooves formed in the corresponding partitions, respectively.