We aimed to record and visualize the investigation activities of search and rescue dogs. The dog’s trajectory is required to create this visualization, and the dog’s velocity needs to be determined to estimate its trajectory. In this study, we examined a method for velocity estimation that uses a dog’s gait. We measured a Labrador dog’s gaits (walk and trot) and analyzed the gait data. From the gait data, we found that there are cyclic moments when the dog’s velocity vector faces its heading direction. This fact enables the reconstruction of the velocity vector v =(vx, vy, vz)T from the dog’s speed |v| and pose. We devised a precise estimation method for a dog’s velocity and evaluated its accuracy. From the evaluation results, we confirmed that the gait-based velocity estimation was more accurate than velocity estimation based on the extended Kalman filter when |v| was obtained at 1, 5, and 10 Hz. This result can pave the way for using a mobile phone to estimate a dog’s trajectory.