Born in Tokyo, Japan on October 12 1946 as a son of a jazz band leader and pianist, Yoshiaki Masuo grew up surrounded by jazz music, although he never had any formal musical training. At the age of 15, he started playing the guitar on his own. Prominent among his early influences were Wes Montgomery and Grant Green.
While in Waseda University Jazz Club, Masuo was discovered by alto saxophonist Sadao Watanabe, and joined his group at the end of 1967. Masuo thus started his professional career on top as a regular of Japan's leading jazz group. He was in the group for three years, and experienced tours outside of Japan with Sadao, playing at Montreux and Newport jazz festivals. He was 1970's number one guitarist in the readers' poll of Swing Journal, Japan's most popular jazz magazine. He won the readers poll in the following years even after leaving Japan, five times in total.
Masuo moved to New York City on June 13, 1971. There he played with Teruo Nakamura, Lenny White, Michael Brecker, Chick Korea, Elvin Jones (Masuo took part in the recording of Merry Go Round) . He also played as a regular of Ashford and Simpson. In 1972, he was a member of Lee Konitz's group.
In the spring of 1973, he joined the Sonny Rollins group. He was with Sonny three years the first time and three years more from 1981. He toured with the group all over the United States as well as Japan and Europe. He participated in the recording of five Rollins' albums including The Cutting Edge (of the five, one is released in Japan only, and another in Europe).