He was an emeritus professor of the University of Tsukuba after his retirement and continued his involvement in mycological research.
[5] His studies of fungal taxonomy included ways to improve identification methods.
In the early 1960s he was involved in development of the Hughes–Tubaki–Barron System for classification of anamorphic fungi that was in use from 1968 onwards, in collaboration with Stanley Hughes and G.L.
This was based on the mechanism of conidial development, viewed using light and electron microscopy, rather than relying on the final form of the conidia alone.
The International Mycological Association named the Keisuke Tubaki Medal after him, awarded for achievement by an Early Career Researcher based in Asia.