The present invention relates to a beta-galactosidase mutant having high transglycosylation activity and containing a C-terminal deletion, and the use thereof and more. More specifically, the present invention relates to a beta-galactosidase mutant having a C-terminal deletion, a gene encoding the same, a recombinant vector containing the gene, a recombinant microorganism transformed with the gene or the recombinant vector, and a method for producing the beta-galactosidase mutant using the recombinant microorganism. Using the high transglycosylation activity of the beta-galactosidase mutant containing the C-terminal deletion according to the present invention, galactooligosaccharide can be efficiently produced in large amounts.