The effect of added BN on the electro-magnetic properties and enhanced room temperature magnetoresistance in (1-x)La0.7Ca0.2Sr0.1MnO3 (LCSMO)+x(BN) composites has been studied systematically. The results of X-ray diffraction (XRD) and SEM show that BN and LCSMO coexist in the composites and BN mainly goes into the grain boundary region without any chemical reaction with LCSMO. The results of electronic measurements show that the intrinsic insulator-metal transition temperature (TP) does not change, which is in accordance with the results for the Curie temperature TC. It is interesting to note that an enhanced magnetoresisitance (MR) effect for the composites is found over a wide temperature range from low temperature to room temperature in an applied magnetic field of 3 kOe. These phenomena can be explained by considering that BN, which segregated at the grain boundaries or surfaces, does not change the intrinsic structure of LCSMO. We argue that the introduction of BN gives rise to magnetic disorder and hence an enhanced tunnelling effect, which is responsible for the MR enhancement.