Capacity of wireless communication systems can be increased enormously using arrays of antenna at transmitter and receiver. In these so called multi-input multi-output (MIMO) communication systems, the performance of symbol detection methods is tightly related to the channel knowledge at the receiver side. Practically, the channel information at the receiver is subjected to error because of the outdated data, quantization error, and imperfect channel estimation/measurement. It is known that in the case of imperfect channel knowledge, performance of symbol detection in MIMO communication systems may severely degrades. In this paper, we briefly address the effect of channel estimation error on the performance of sphere detector in MIMO communication systems. We analytically propose and study two detection methods to improve the performance of sphere detector when the channel matrix is imperfectly known at receiver. In our proposed robust method, the sphere detection algorithm is modified while a small computational complexity is added to the detector.