Gustaf af Geijerstam (1858–1909) was a Swedish novelist. He was a friend of August Strindberg's. Many of his works were translated into German during his lifetime, and one, Äktenskapets komedi (1898), was reviewed favorable by Rainer Maria Rilke, who remarked that Geijerstam was an author "one must follow attentively from book to book." Only two of his novels were translated into English: Boken om Lille-bror (1900), as "the Book about the Little Brother" in 1921, and Kvinnokraft (1901), as "Woman Power" in 1922. Other works include Erik Grane (1895), Karin Brandts dröm (1904) and Medusas hufvud (1905).