An optical subassembly testing system includes a pedestal, a rotation device, a holder and a supporting device. The rotation device includes a rotation member, a connecting plate and a retractable pillar. The rotation member is arranged on the pedestal and rotates relative to the pedestal. The connecting plate includes a mounting portion and a protruding portion, the mounting portion is arranged on the rotation member, the protruding portion extends away from the mounting portion and is exposed outside of the rotation member, and the retractable pillar is fixed perpendicular to the pedestal on an end of the protruding portion. The holder is fixed on an end of the retractable pillar and clamps a fiber connector. The supporting device includes a plurality of receiving grooves surrounding the pedestal, the receiving grooves are configured for receiving transmitter optical subassemblies (TOSAs) to test by aligning the fiber connector with each TOSA in turn.