The calnexin homologue (Cne1p) of Saccharomyces cerevisiae was expressed in Escherichia coli to evaluate its chaperone function. The chaperone function was examined as to the effects on the suppression of thermal denaturation and the enhancement of refolding, using citrate synthase (CS) as a nonspecific chaperone substrate. Cne1p effectively suppressed the thermal denaturation of CS and enhanced the refolding of thermally or chemically denatured CS in a concentration-dependent manner. In addition, the chaperone function of Cne1p was greatly affected in the presence of monoglucosylated oligosaccharides (G1M9) that specifically bind to the lectin site. These results indicated that Cne1p functions as a molecular chaperone in Saccharomyces cerevisiae.