Transgenic tobacco plants exhibiting exogenous cellulase activity were produced by introduction of a truncated cellulase (t-EgI) gene from Ruminococcus albus. They accumulated about 0.1-0.5% t-EgI of the total soluble proteins in the cytoplasm. They were normal in morphology and growth. t-EgI expressed in the transgenic plants degraded their own cell wall materials after the cells were disrupted. The plants expressing the t-egI gene could be used as "cellulase-encapsulating plants" for livestock and food industries.