Bretnor’s father, Grigory Kahn, was born in Russia, but he and his family left Siberia for Japan in 1917 and later settled in the United States. Bretnor’s mother was born a British subject, became a Russian subject, spent from 1917 to 1920 in Japan, then settled in the United States with her children Reginald and Margaret. Reginald Bretnor himself was born in Vladivostok, Russia. He was married to Helen Harding, a translator and U.C. Berkeley librarian, from 1948 until her death in 1967. He subsequently married Rosalie, whom he referred to in a letter in the Southern Oregon Historical Society Archives as Rosalie McShane, although she wrote under the name Rosalie Bodrero.