An experimental study of the mode of downward burning zone spread in an opposed gas flow was conducted for two cellulose materials of cylindrical shape. The ranges of the two modes, i.e., of flame spread and smolder spread, were examined as functions of the oxygen concentration and velocity of the flow, for several cylinder diameters. The variation of the burning zone spread rate with flow velocity was also examined for typical cases. For both materials, with an increase in flow velocity, the upper limit of oxygen concentration for smolder spread decreased whth the lower limit of oxygen concentration for flame spread or smolder increased; the range of the oxygen concentrations where both flame spread and smolder spread occur shrank as the flow velocity increased. However, the nature of the variations of these critical values with flow velocity or cylinder diameter depended on the kind of material. The relation between the dependence on the flow velocity of the flame-spread rate and that of the smolder-spread rate at the same oxygen concentration also differed between these materials. From the observation of the spreading burning zone, it was found that under certain conditions near the flame extinction limit, spread of flame is accompanied by an intense char oxidation reaction. The results of the experiment are discussed primarily in the light of global controlling mechanisms of burning zone spread.