Mevalonate kinase is one of ATP-dependent enzymes in the mevalonate pathway and catalyzes the phosphorylation of mevalonate to form mevalonate 5-phosphate. In animal cells, it plays a key role in regulating biosynthesis of cholesterol, while in microorganisms and plants, it is involved in the biosynthesis of isoprenoid derivatives that are one of the largest groups of natural products. Crystal structure and sequence alignment show that a unique disulfide bond exists in mevalonate kinase of thermostable species Methanococcus jannaschii, but not in rat mevalonate kinase. In the present study, we investigated the effect of the disulfide bond in M. jannaschii mevalonate kinase and an engineered disulfide bond in rat mevalonate kinase mutant A141C on the properties of enzymes through characterization of their wild-type and variant enzymes. Our result suggests that the Cys107-Cys281 disulfide bond is important for maintaining the conformation and the thermal activity of M. jannaschii mevalonate kinase. Other interactions could also have contributions. The thiol-titration and fluorescence experiment further indicate that rat mevalonate kinase A141C variant enzyme has a new disulfide bond, which makes the variant protein enhance its thermal activity and resist to urea denaturation.