PURPOSE: To provide a separation membrane excellent in O2-permeability, chemical resistance and mechanical strength, constituted of a polyurea/polysiloxane copolymer wherein a polysiloxane structure is introduced into the main chain of polyurea and a perfluoroalkyl group is introduced into the side chain thereof.

CONSTITUTION: A separation membrane comprises a substantially linear polyurea/polysiloxane polymer having a repeating unit represented by formula I [(wherein R1 is bivalent hydocarbon, R2s are respectively independently monovalent alkyl or an aromatic group, (m) is an integer of 2W4 and (n) is an integer of 1 or more] and a repeating unit represented by formula II [wherein R1 is same to the aforementioned group, R3 is (P+2)-valent hydrocarbon or a heterocyclic group, Z is -O(CH2)x- or COO(CH2)x-, Rf is 1C or more perfluoroalkyl, (p) is 1 or 2 and (x) is 0 or an integer of 1 or more].