Tobacco (Nicotiana tabacum L.) cells were transformed with rice expansin genes, OsEXPA4, OsEXPB3, OsEXPB4, and OsEXPB6, to elucidate the function of the genes in tobacco cells. The transformation increased the mass of the callus by $36\%-65 \%$, and the cell length by $12\%-28\%$. The cell width was decreased by $3\%$ for OsEXPB3, not changed for OsEXPB4, increased by $25\%;and;20\%$ for OsEXPA4 and OsEXPB6, respectively. From database search, seven expansin genes were found and six of them belong to EXPA group and one of them belongs to EXPB group. EXLA and EXLB were not found. All tobacco expansin genes were evenly distributed in the phylogenetic tree of rice and Arabidopsis expansin genes.