The present invention relates to transgenic plants for producing cellulose by a mechanism of autohydrolysis and a method producing soluble sugars using them, more particularly to transgenic plants transformed with recombinant cDNA coding cellulase, cellulose binding domain and chloroplast targeting peptide and a method producing soluble sugars using them. Transgenic plants and a method producing soluble sugars using them would be a highly cost-effective system for the production of soluble sugars on a large scale.