Study Design. Painful behavior testing, whole-cell patch clamp recordings, and PCR analysis were served to test the influence of T-type Ca2+ channels in spinal nerve-injured rats. Objective. To determine the changes of T-type Ca2+ channels in dorsal root ganglion (DRG) neurons of different sizes and the contribution to neuronal firing and painful behavior in neuropathic pain induced by nerve injury. Summary of Background Data. T-type and high-voltage-activated Ca2+ channels play an important role in the transmission of nociceptive signals, especially in neuronal hyperexcitability in neuropathic pain. However, little is known about how nerve injury affects T-type Ca2+ channels in DRG neurons of different sizes. Methods. The effect of intrathecal administration of mibefradil in nerve-ligated rats was examined by painful behavior testing and current clamp. The changes of T-type Ca2+ channels in DRG neurons caused by spinal nerve ligation were determined by RT-PCR analysis and voltage clamp. Results. Spinal nerve injury significantly increased current density of T-type Ca2+ channels in small DRG neurons. In addition, nerve injury significantly increased the percentage of T-type Ca2+ channels in medium and large DRG neurons. Nerve injury significantly increased the mRNA levels of Cav3.2 and Cav3.3 in DRGs. Block of T-type Ca2+ channels on mibefradil administration significantly normalized painful behavior and hyperexcitability in neuronal firing in spinal nerve-injured rats. Conclusion. Our study first indicated the upregulation of functional T-type Ca2+ channels in DRG neurons of different sizes and the changes in different subtypes of T-type Ca2+ channels by spinal nerve injury. Considering the effect of blocking T-type Ca2+ channels in painful behavior and abnormal neuronal firing in rats with nerve injury, our results suggest that T-type Ca2+ channels are potential therapeutic targets for the treatment of spinal nerve ligation-induced neuropathic pain.