This paper presents both theoretical and experimental studies on evaluating dynamic responses of the moored object and the mooring lines in regular waves. This time domain method treats the mooring line as lumped parameter system of discrete masses and considers the mutual interaction of dynamic response between the moored body and the mooring lines. Numerical results for the motions of the moored body and the dynamic mooring tensions were obtained and are compared with experimental data with excellent agreement. As a result of this study, it is found that the dynamic effect on the mooring tension is significant when the floating body is moored and may influence on the body motion considerably unless the body is large enough in size. Secondly, the effect of this dynamic tension on the moored body motions becomes large comparing with that of the nonlinearity of the mooring restoration in case that the mooring line is heavy. Therefore, it is concluded that the dynamic analysis of the mooring line is important for the analysis of the moored body motion and for the design of the mooring system.