The gamma-gamma coincidence counting method with two coaxial Ge detectors was applied to the absolute measurement of radioactivity. To investigate the dependence of the calculated activity on the coincidence time, a 60Co standard point source was measured by a gamma-gamma coincidence counting system. As a result, it was confirmed that the coincidence time did not influence the calculated activity, which agreed with the calibrated value within 10%. To estimate measurable range of source disposition, two or nine 60Co sources were measured by this system. As a result, the measurable range was 3cm × 10cm × 10cm(thickness × width × height), when the detector-detector distance was 10cm.