An 8-months-old young Maltese bitch was presented for investigation of anorexia and occasional vomiting. The body weight was 2 kg. Abdominal sonography demonstrated abnormal enlargement of uterus. The dog had been clinically and pathologically examined. Also, ovariohystectomy was performed. Staphylococcus aureus was identified in the pus-like materials of the uterine lumen. This case was confirmed as pyometra induced by Staphylococcus aureus. Gross examination of the dissected uterus revealed enlarged uterine horn, which had yellowish or brownish pus-like materials in the lumen. Also, there was several segments formation between the enlarged areas of left and right uterine horns. Histopathologically, endometritis and necrosis were present in uterine wall. The bitch made a complete recovery following an ovariohystectomy. This case was spontaneous pyometra induced by Staphylococcus species. On our knowledge, this is a very rare report of pyometra occurrence in young dog and Staphylococcus species-induced pyometra. This study may provide a valuable data on the study of canine pyometra.