Oh's 868 home runs in Japan set an all-time pro baseball record. The son of a Chinese father and a Japanese mother, he had trouble gaining acceptance with Japanese fans after signing for a $60,000 bonus as a pitcher. Switched to first base, he couldn't hit the curveball until he took up samurai swordsmanship as a practice method; he adopted a foot-in-the-air stance similar to Mel Ott's, though he was unaware of Ott's existence. He was noted for taking 30 to 40 minutes of batting practice a day
In 1965 Oh set the Japanese record of 55 HR in a 140-game season. His record of 54 HR for the revised 130-game schedule was tied by Randy Bass in 1986. He averaged 45 HR a year in winning 13 consecutive HR titles. On the dominating Yomiuri Giants, Oh batted third and Shigeo Nagashima hit clean-up as Japan's equivalent of Babe Ruth and Lou Gehrig. Oh won triple crowns in 1974 and 1975. He broke Hank Aaron's career HR mark in 1978, but Aaron, six years Oh's senior, out-homered him in contests held in 1974 and 1984. Oh became Yomiuri's manager upon retirement.