The present study investigated the roles of cross-hemispheric communication in promoting left-lateralization of syntactic processing in the brain. Fifty-six young right-handers without familial sinistrality background underwent a divided visual field ERP grammaticality judgment experiment to assess syntactic responses from each hemisphere. Two behavioral tasks--bilateral flanker task and bilateral word-association task, were used to assess cross-hemispheric inhibition and transmission delays. The grand average ERP data showed a significant unilateral P600 grammaticality effect in the left hemisphere only. However, individual variations in the P600 responses were observed in both hemispheres. Results of correlational analyses showed that larger LH P600 effects were associated with slower inter-hemispheric transmission, and that smaller right hemisphere (RH) P600 effects were associated with more effective LH-on-RH inhibition. These results yielded support for both the callosal distance and inhibition hypotheses for language lateralization and demonstrated that different aspects of cross-hemispheric communication jointly influence the degree of syntactic lateralization.