Three cellulase [EC 3.2.1.4, β−1, 4-glucan glucanohydrolase] components were obtained from Meicelase, a commercial product from Trichoderma viride. The purification was carried out through consecutive column chromatography. Each cellulase showed a single peak in ultracentrifugal pattern, and the sedimentation coefficients were 3.54S, 3.75S and 3.62S, respectively. Their amino acid compositions resembled each other in respect of high contents of acidic amino acids, glycine, serine and threonine, and of low contents of basic amino acids and sulphur containing amino acids. They contained carbohydrates in an amount of 10—15%, which appears to consist of several neutral sugars and glucosamine. The optimal activities of the three cellulases were similarly found to be at pH 4.5–5.2, but their heat stabilities were different from each other. The three cellulases hydrolyzed, with different spectra, a series of substrates including several cello-oligosaccharides, CMC and various insoluble celluloses such as Avicel and absorbent cotton, but showed no activities toward cellobiose and aryl β-glucoside.