The Gαq-containing G protein, an important member of Gq/11 class, is ubiquitously expressed in mammalian cells. Gαq has been found to play an important role in immune regulation and development of autoimmune disease such as rheumatoid arthritis (RA). However, how Gαq participates in the pathogenesis of RA is still not fully understood. In the present study, we aimed to find out whether Gαq controls RA via regulation of Th1 differentiation. We observed that the expression of Gαq was negatively correlated with the expression of signature Th1 cytokine (IFN-γ) in RA patients, which suggests a negative role of Gαq in differentiation of Th1 cells. By using Gαq knockout (Gnaq-/-) mice, we demonstrated that loss of Gαq led to enhanced Th1 cell differentiation. Gαq negative regulated the differentiation of Th1 cell by modulating the expression of T-bet and the activity of STAT4. Furthermore, we detected the increased ratio of Th1 cells in Gnaq-/- bone marrow (BM) chimeras spontaneously developing inflammatory arthritis. In conclusion, results presented in the study demonstrate that loss of Gαq promotes the differentiation of Th1 cells and contributes to the pathogenesis of RA.