Molar cyclization equilibrium constant (K$_{x}$) of poly(alkylene terephthalate) (PAT) cyclics was calculated by the Monte Carlo simulation on the basis of rotational isomeric state (RIS) model. The experimental $K_{x}$ of PAT cyclics, which was not clearly explained by the Jacobson-Stockmayer theory and the method of Flory, Suter, and Mutter however, was explained well by the direct computational method with the reaction radius ${gamma}$=0.5 < ${gamma}^{2}$> $^{1/2}$. The effect of PAT conformation on $K_{x}$ of PAT cyclics was investigated by changing its statistical weight parameters, ${sigma}_{1}$ and ${sigma}_{2}{cdot}K_{x}$ of PAT cyclics obtained by the direct computation method with various radii and the radius ${gamma}$=0.5 < ${gamma}^{2}$> $^{1/2}$ was slightly changed with ${sigma}_{1}$ and ${sigma}_{2}$. Consequently, it was concluded that $K_{x}$ of PAT cyclics is strongly dependent on the configuration of each PAT and affected by the change of its conformation to some extent.