The pyrolysis of pure and fire retarded bulk cellulose samples in a nitrogen atmosphere is studied. Sodium hydroxide is used as the fire retardant. The study is directed toward determining the effects of the solid phase fire retardant on the burning of cellulose. The material property of pure and fire retarded cellulose which most directly affects its burning behavior, the heat of gasification, is measured by using a specially designed pyrolyzing chamber. Theoretical results are obtained for a one-dimensional pyrolisis wave propagating into cellulose by using a finite-difference calculation. The experimental results are in qualitative agreement with the computations, but give a lower value for the heat of gasification. The experimental data show that sodium hydroxide acts as a catalyst in the pyrolysis of cellulose. Its addition leads to decreases in the heat of gasification and the mass fraction of noncombustible volatiles, and to increases in stoichiometric ration and the heat of combustion of combustible volatiles, thereby has a dual effect on cellulose burning.