Three conmmercial cellulases prepared from Penicillium notatum(cellulalse[K]), Trichoderma viride(cellulase[J]) and Aspergillus niger(cellulase[A]) were nalyzed with respect to their relative purity, activity and the effects of several metal ions on their activities. The activity of cellulase[K] was the strongest of all and that of cellulase[A] being the weaker. The purity of cellulalse[K] was the highest while that of cellulase[J] was the lowest. Under the assay conditions, the optimum concentrations of $Zn^{++}$ and $Mg^{++}$ ions for the activity of cellulase[K] was the highest while that of cellulase[J] was the lowest. Under the assay conditions, the optimum concentrations of $Zn^{++}$ and $Mg^{++}$ ions for the activity of cellulalse[K] was the highest while that of cellulase [A] being weaker. The purity of cellulase[K] was the highest while that of cellulase[J] was the lowest. Under the assay conditions, the optimum concentrations of $Zn^{++}$ and $MG^{++}$ ions for the activity of cellulase[K] were 2 and 7mM while those of cellulase[A] were 5 and 6 mM respectively and those of cellulase[J] were 3mM for both ions. Cellulase[K] and cellulase[J] were more strongly activated by $Zn^{++}$ than $Mg^{++}$ and cellulase[J] by $Mg^{++}$ than $Zn^{++}$. Both $Cu^{++}$ and $Mn^{++}$ ions inhibited by these metal ions. the inhibitory effects of $Mn^{++}$ ions for enzyme activities were stronger than $Cu^{++}$ ions. The Ki values of $Cu^{++}$ and $Mn^{++}$ for cellulase[K] were found to be 6.1 and 0.7mM, those of cellulase[J] were 2.6 and 0.32 mM, and those of cellulalse[A] were 2.0 and 0.2 mM respectively. Both $Cu^{++}$ and $Mn^{++}$ ions showed a pattrn of competitive inhibition of the enzyme activity. When Na-CMC was used as substrate, the Km and V values of celluase [K] were calculated to be $2.0{ imes}10^{-4}mM$ and 3.43mmoles/hour, those of cellulase[J] were $2.4{ imes}10^{-4}mM$ and 3.77mmoles/hour, and those of cellulase[A] were $4.0{ imes}10^{-4}mM$ and 4.00mmoles/hour respectively.