In this paper, at first the relation between the optimum interferences and the fatigue limit have been exmained when the press-fit of bushings are represented by interferences. Then the influences of the number of links on the fatigue strength have been examined, and studied statistically. The results are as follows: (1) The effects of the press-fit of bushings could be estimated by fatigue limit diagram of roller link-plates without interference. (2) The optimum interference exists that gives the most improved fatigue limit of roller chains. (3) The fatigue limit of any number of links could be estimated statistically by the life distribution of roller link-plates. (4) The tensile strength, the fatigue strength at N cycles and the fatigue limit decrease, as the number of links increases. And the ratio of decrease is in order of fatigue limit, fatigue strength at N cycles and tensile strength.