A 3-week exposure test of the C-ring specimen sampled from a commercial phosphorous deoxidized copper tube in ammoniacal environment were carried out to investigate stress corrosion cracking of a pure copper tube. C-ring specimens were applied high and low stresses; a high stress was over a proof stress, whereas a low stress was within an elastic region. Stress corrosion cracking occurred in the highly stressed C-ring specimen after the 3-week exposure test in gas-phase ammonia derived from 3 and 9wt% ammonia water. On the other hand, intergranular corrosion was observed in the C-ring specimens under low stress. A diameter recovery rate of C-ring specimen for which stress corrosion cracking developed was smaller than that of C-ring specimen without stress corrosion cracking.