The magnetocaloric effect is a well-known phenomenon, which can be applied to develop a system for the magnetic conversion of heat to work or automatic cooling of a working fluid without any mechanical pump. A prototype of a miniature automatic cooling device is established, which is mainly composed of a temperature-sensitive magnetic fluid, a permanent NdFeB magnet, heat sources and heat sink. A series of experiments are conducted to investigate the feasibility, the performance capacity of the cooling device. A model for simulating the operation process is provided and the principle of parameter estimation is applied to determine the flow velocity of the fluid in the loop. The effects of several factors such as the external magnetic field and the temperature distribution of the magnetic fluid on the cooling performance of the device are discussed. (C) 2008 Published by Elsevier Ltd.