Polysilazane is treated with a single or mixed solvent comprising one or more members selected from the group consisting of xylene, anisole, decalin, cyclohexane, cyclohexene, methylcyclohexane, ethylcyclohexane, limonene, hexane, octane, nonane, decane, a C8-C11 alkane mixture, a C8-C11 aromatic hydrocarbon mixture, an aliphatic/alicyclic hydrocarbon mixture containing 5 to 25% by weight of C8 or more aromatic hydrocarbons, and dibutyl ether, wherein the number of 0.5 micron or more fine particles contained in 1 ml of the solvent is 50 or less. As the treatment of polysilazane, there are illustrated, for example, edge-rinsing and back rinsing of a polysilazane film formed by spin coating polysilazane on a semiconductor substrate. The water content of the solvent is preferably 100 ppm or less.