Self-sustainable oscillating motions of the slug flow in oscillating heat pipes have been investigated in the paper. A mass -spring model in the adiabatic section of the heat pipe under the exciting sources in its evaporator and condenser is applied to describe the oscillating characteristics of the two-phase flow in the serpentine capillary channels of the heat pipe. The effects of geometry of channels, properties of working fluid, capillary force, heating power, and gravity on the oscillating motions of the working fluids in the heat pipes were examined. Thermoacoustic theory is applied to calculate heat transport through the adiabatic section of the heat pipes. The experimental investigation of a prototype of the oscillating heat pipe was conducted. Numerical and experimental results relevant to the heat transport capability of the heat pipe were analyzed and compared. Oscillating motions of vapor bubbles and liquid slugs may dramatically enhance heat and mass transfer in the capillary channels of the heat pipes. For each capillary channel of the heat pipe, large quantities of heat will be transferred radially and hence transported axially. Recirculation of the working fluid, especially in short liquid plugs, may significantly improve the heat transport capability of the heat pipe.