He was married to Marian Koshland ( née Elliot), a fellow UC Berkeley professor, from 1946 until her death in 1997. Marian was a gentile , the daughter of a teacher who had immigrated from Denmark and a hardware salesman father of Southern Baptist background.  Daniel and Marian had five children: Ellen Koshland, Phyllis "Phylp" Koshland, James Koshland, Gail Koshland, and Douglas Koshland .  Koshland's son Douglas Koshland is a professor of genetics at UC Berkeley.  Donald Koshland supported the creation of the Marian Koshland Science Museum by giving a major gift to the National Academy of Sciences in Marian's honor.