Previous studies have demonstrated that the left hemisphere was specialized in language function using functional magnetic resonance imaging (fMRI). On the other hand, some studies have revealed that the right hemisphere was related with language function. The hypotheses of this study were that (1) the regions related with language function have a bilateral functional network and (2) the level of functional connectivity is dependent on the hearing conditions. To test these hypotheses, the participants were instructed to select the a numeric word (e.g., thirty or thirteen) after they heard an auditory sentence which was presented to both ear (BH), only to the left ear (MHL), or only to the right ear (MHR). To identify the brain regions related with speech perception, the general linear model (GLM) to estimate the neuronal activation and functional connectivity (FC) analysis were conducted. The results of this study showed that the right superior temporal gyrus (STG) was involved in language function. The right STG had showed the significant level of FC with the left STG. Furthermore, the level of bilateral FC was significantly diminished and the accuracy of correct word selection was significantly decreased in MHR condition compared to BH condition. These results may indicate that bilateral network within STG is related with speech perception.