The effects of $eta$-(1,6)-galactosyl trehalose trisaccharide ($eta$-GT) that was preferentially produced by Escherichia coli $eta$-galactosidase on cryo- and thermo-protections of protein were investigated with those of other sugars at the level of 8% (w/v). As compared to a control without sugar additive, $eta$-GT effectively enhanced 32-54% of the cryoprotection of fish actomyosin against repeated freeze-thawing and frozen storage, and also 49% of the protection against thermal inactivation of pyrophosphatase, respectively. As a result, it was significantly more effective than sorbitol and trehalose in both cryoprotection and thermoprotection. Thus, $eta$-GT would be possibly applied as a sugar substitute for cryo- and thermo-protective applications of food protein.