The purpose of this paper is to investigate experimentally the strength and deformation of T-joints to evaluate the structural behavior of truss connection consisted in square hollow steel section. There are the Square type and Lozenge type in T-joint shapes. Principle parameters are the ratio of the chord width to thickness(D/T=33.3, 25, 16.7) and the ratio of brace width to chord width(d/D=0.4, 0.5, 0.67, 0.83, 1.0). The most important result obtained from this experiment is as follows ; The strength of T-joints increase proportionally as the D/T ratio decrease, and the d/D ratio increase. The others, experimental results are summarized for strength to displacement, initial stiffness and failure mode of each T-joints.