G-protein-coupled receptors (GPCRs) may form homomeric or heteromeric complexes and cooperatively mediate intracellular responses. Previously, we showed modulation of type 1 metabotropic glutamate receptor (mGluR1) function by metabotropic gamma-aminobutyric acid receptor (GABA_BR) in cerebellar Purkinje cells. The activity of mGluR1 is mediated by a G_q protein, and has a crucial role in synaptic plasticity and motor learning. GABA_BR inhibits neuronal activity through G_i protein, which regulates the release of neurotransmitters and the activity of ion channels. In this report, we investigated in greater detail the relationship of these GPCRs using non-neuronal cells. Using live cell imaging and biochemical analysis, we showed that mGluR1 and GABA_BR form complexes at the cell surface. Moreover, using cAMP homogenous luminescence assay and calcium imaging, we found that mGluR1 and GABA_BR regulate their signal transduction of each other. These findings provide a new insight into neuronal GPCR signaling and demonstrate a novel regulatory mechanism of synaptic transmission. This interaction would be involved in several important physiological and pathophysiological functions related to mGluR1 and GABA_BR, such as cerebellar motor learning and its dysfunction.