This work experimentally investigated the fluid flow and heat transfer behaviors of jet impingement onto the rotating heat sink. Air was used as impinging coolant, while the square heat sinks with uniformly in-line arranged 5 x 5 and 9 x 9 pin-fins were employed. The side length (L) of the heat sink equaled 60 mm and was fixed. Variable parameters were the relative length of the heat sink (L/d = 2.222 and 4.615), the relative distance of nozzle-to-fin tip (C/d = 0-11), the jet Reynolds number (Re = 5019-25,096) and the rotational Reynolds number (Re-r = 0-8114). Both flow characteristics of stationary and rotating systems were illustrated by the smoke visualization. Besides, the results of heat transfer indicate that, for a stationary system with a given air flow rate, there was a larger average Nusselt number (Nu(0)) for the 9 x 9 pin-fin heat sink with L/d = 4.615 and C/d = 11. For a rotating system, a bigger Re-r meant a more obvious heat transfer enhancement (Nu(Omega)/Nu(0)) in the case of smaller Re, but Nu(Omega)/Nu(0) decreased with increasing Re. In this work, Nu(Omega)/Nu(0) in L/d = 2.222 is higher than in L/d = 4.615; among the systems in L/d = 2.222, bigger Nu(Omega)/Nu(0) exists in the case of C/d = 9-11, but among the systems in L/d = 4.615, bigger Nu(Omega)/Nu(0) exists in the case of C/d = 1-3. Finally, according to the base of Nu(Omega)/Nu(0) >= 1.1, the criterion of the substantial rotation was suggested to be Re-r/Re >= 1.154. (C) 2008 Elsevier Ltd. All rights reserved.