With an increasing capacity of large marine engines, the axial vibration of a large ship propeller shaft becomes a new problem. In order to solve this, investigation of the dynamic characteristics of thrust bearings is necessary. The authors theoretically analysed the variation of the oil film thickness and the pressure distribution of hydrodynamic thrust bearings under periodical load and verified the results experimentally. In the theoretical calculation, two different ;methods were used. One of them is a strict method, in which the Reynolds equation is solved at every small time interval (nonlinear solution), and the other is an approximate method, using spring and damping coefficients of the oil film (linear solution). The results are: (1) The linear solution method can be applied up to a considerably large amplitude of load. (2) Phase delay of the oil film thickness against the load is large, which has been verified both analytically and experimentally.