Transient receptor potential melastatin 2 (TRPM2) is a Ca²⁺-permeable, non-selective cation channel that is activated by oxidative stress such as reactive oxygen species (ROS) and pyridine nucleotides such as adenosine diphosphate (ADP) ribose. TRPM2 channels are widely expressed in leukocytes, and TRPM2-mediated ROS-sensitive Ca²⁺ signaling play a crucial role in a number of cellular processes and functions. In this study, transcript of TRPM2 was cloned from canine peripheral blood mononuclear cells (PBMCs) and some of functional properties of canine TRPM2 were analyzed in vitro. In canine TRPM2 sequence, the basic structure of TRP channel and the binding sites for ADP ribose in MHR1/2 and NUDT9-H domains were conserved. We analyzed the reactivity of heterologously expressed canine TRPM2 to hydrogen peroxide (H₂O₂) in Ca²⁺-imaging experiments. Canine TRPM2 was activated by H₂O₂ in a concentration-dependent manner. This reaction was inhibited by perfusion of TRPM2 inhibitor 2-APB or Ca²⁺-free extracellular solution. Next, canine PBMCs were incubated with H₂O₂ and were subjected to RT-qPCR analysis. The expression of an anti-inflammatory cytokine IL-10 was not enhanced, but the expression of inflammatory cytokines IL-1β, TNFα, and IL-8 (CXCL8) were tended to be enhanced after incubation with H₂O₂. Our results suggest that TRPM2 plays an important role in activation of canine leukocytes, and that TRPM2 is a possible target for regulation of leukocytes functions.