G protein-coupled receptors (GPCRs) transduce their signaling through the activation of trimeric G proteins. The signaling is modulated by the interacting proteins with GPCRs, but the regulatory mechanisms are diverse and largely unknown. Parathyroid hormone receptor (PTHR) activates G_s, which in turn transduces adenylyl cyclase type 6 (AC6)/cyclic AMP (cAMP) pathway. We have previously shown that Tctex-1 (or DYNLT1) interacts with the carboxyl-terminus of PTHR. However, the role of Tctex-1 on PTHR/G_s signaling has remained unresolved. In the present study, we first found that knockdown of Tctex-1 did not alter the cell surface expression of PTHR without PTH-(1-34) stimuli in HEK293 cells stably expressing HA-tagged PTHR. In contrast, PTH-(1-34)-induced cAMP production was dramatically decreased by knockdown of Tctex-1. The Tctex-1-knockdown also suppressed cAMP production mediated through endogenous PTHR in MC3T3-E1 preosteoblast cells. Cyclic AMP production mediated through both PTHR and PTHR-KRVS mutant, which cannot bind to Tctex-1, was equally suppressed by Tctex-1-knockdown in HEK293 cells. The data indicate that the binding of Tctex-1 to PTHR is not a prerequisite for promoting cAMP production by Tctex-1. Moreover, cAMP production induced by forskolin, a direct AC activator, was reduced by Tctex-1-knockdown in HEK293 and MC3T3-E1 cells, suggesting that Tctex-1 augments AC activity. Finally, we found that Tctex-1 directly binds to AC6 in vitro. In summary, our results demonstrate that Tctex-1 augments PTHR/G_s/AC6 signaling through direct activation of AC6.