In some regression model, the mean square errors of a ratio estimator, a grouped jackknife estimator, and an estimator based on the least square estimators (LSEs) are obtained and compared up to the order O(n^-3), where n is the size of the sample. The bias-adjusted ratio estimator and the jackknife estimator are also compared up to the order O(n^-3). Then it is concluded that the estimator based on the LSEs is an asymptotically better estimator of ratio up to the order O(n^-3). Some examples are given.