PURPOSE: To obtain a gas separation composite membrane excellent in separability and permeability and also having good durability, by providing a gas permeable polymer layer and a silicon atom-containing polyarylene oxide layer on a porous support.

CONSTITUTION: A porous support having fine pores with a pore size of 10W 10,000 is used. A layer comprising a polymer having gas permeability and a layer comprising polyarylene oxide containing a silicon atom are provided on said support. The former layer has oxygen transmission coefficient of at least 10-9cm3cm/cm2seccmHg and the thickness thereof is pref. 0.01W3μm while the latter layer is formed by using polyarylene oxide having an organosilil group. At least one organosilil group is necessarily contained per 1W98% of the constitutional unit of polyarylene oxide. The thickness of the latter layer is pref. 0.01W1μm.