In this article, the conformational properties and elastic behaviors of ring polymers in the process of tensile elongation are investigated with the Monte Carlo method and the bond fluctuation model. The ratio of the mean-square diameter to the mean-square radius of gyration increases with the elongation ratio, lambda, and the instantaneous shape of ring polymers is more symmetric than that of linear chains in the process of tensile elongation. Here for ring polymers rather than the mean-square end-to-end distance for linear polymers is defined as the average of squared distances between two segments separated by N/2 bonds, where N represents the total number of bonds. Local quantities, that is, the mean-square bond length and the mean bond angle increase with A, especially for short ring chains. The and have the same relationship with the chain length, N, that is, similar to N (1.130+/-0.020) and similar to N (1.160+/-0.013) for a different lambda. Some thermodynamics properties are also addressed here. The average energy per bond decreases with lambda and the average Helmholtz free energy and elastic force f increase with lambda, especially for short ring chains. Comparisons with linear chains are also made. These investigations may provide insight into the elastic behaviors of ring polymers. (C) 2004 Wiley Periodicals, Inc.