In order to study the effect of alloying elements on the spheroidization of lamellar pearlite, quantitative microscopic investigation has been undergone with the four kinds of steel (Fe-C, Fe-C-0.3wt%M; M=Ni, Mn, Cr) by annealing at 700℃. It was found that the rate of spheroidization in described by a cubic law;(1/S)³-(1/S_o)³=K_s·t, where S is the total area of the interface between ferrite and cementite per unit volume, S_o is the initial value and K_s is the rate constant. The K_s is approximated by K_s=K_o/(3f)³, were K_o is the rate constant in Ostwald ripening of cementite particles and f is the volume fraction of cementite. In addition, the fraction of spheroidization X can be described by X=(S_o―S)/S_o for the effect of alloying elements, it was shown that the small additions of Cr, Mn remarkably retared the spheroidization mainly due to the large distribution coefficient between the ferrite and cementite.