In order to understand the fundamental characteristics of thermocapillary convection in an encapsulated liquid bridge, we conducted a series of unsteady three-dimensional numerical simulations of thermocapillary convection in an encapsulated liquid bridge with either 2 or 3 mm inner diameter and 4-7 mm outer diameter as well as variable height 1-3 mm heated from the top wall and cooled at the bottom wall with an adiabatic free surface. Simulation conditions correspond to those in the experiments of Majima ͓S. Majima, Phys. Fluids 13, 1517 ͑2001͔͒. The simulation results indicate that thermocapillary convection in an encapsulated liquid bridge is axisymmetric and steady at the small Marangoni number. However, when the Marangoni number exceeds some critical value, the flow will undergo a transition to three-dimensional oscillatory flow, which is characterized by a standing wave type oscillation, i.e., the periodic growth and decay of temperature disturbances from cold disk to heat disk. The critical conditions for the onset oscillatory flow are determined and compared with the experimental results. The details of the flow and temperature fields are discussed, and oscillation frequencies are also exhibited.