This experiment was carried out to determine the effects of hot environmental temperature in summer and repeated testicular biopsy on semen quality and testicular structure in Korean native goats. The testes of five goats were biopsied repeatedly once a month for 5 months from May 10, 1970. Semen was collected with an electro-ejaculator and artificial vagina, and evaluated once a week from the early June. The volumetric analyses for the testicular structures biopsied were also accomplised. The results obtained were as follows: 1) Repeated testicular biopsy of 5 times in total had no significantly detrimental effects on semen quality through the experimental period. 2) Significant decrease in semen volume, sperm concentration, sperm motility and % alive sperm were observed successively from the early August to the early September. 3) With the increase in pH of semen, high increase of morphologically abnormal spermatozoa(mostly tailless) appeared in all the goats used from the late August to the early September. 4) Between the two methods of semen collection, that is, electro-ejaculator and artificial vagina, there was significant difference in pH of semen, sperm motility, % alive sperm, concentration, but none in the other semen criterial evaluated. 5) The volumetric analysis for the testicular structures showed no significant monthly changes, though slightly fewer spermatids and more lumen were observed in September than in the other months. 6) From the above results, it could be recommended that the breeding male goats be sheltered under slightly coolish environment through the late July to the early September to improved in their fertility in the fall.