The present study was aimed to elucidate the mechanism of stabilization of tubulin by deuterium oxide ($D_2O$). Rate of decrease of tryptophan fluorescence during aging of tubulin at 4$^{circ}C$ and 37$^{circ}C$ was significantly lower in $D_2O$ than in $H_2O$. Circular dichroism spectra of tubulin after incubation at 4$^{circ}C$, suggested that complete stabilization of the secondary structure in D2O during the first 24 hours of incubation. The number of available cysteine measured by DTNB reaction was decreased to a lesser extent in $D_2O$ than in $H_2O$. . During the increase in temperature of tubulin, the rate of decrease of fluorescence at 335 nm and change of CD value at 222 nm was lesser in $D_2O$. Differential Scanning calorimetric experiments showed that the $T_m$ values for tubulin unfolding in $D_2O$ were 58.6$^{circ}C$ and 62.17$^{circ}C$, and in $H_2O$. those values were 55.4$^{circ}C$ and 59.35$^{circ}C$.