The aim of this study was to investigate the efficacy of electronic apex locators to determine the root canal length in teeth of dogs. For this purpose, APIT and ENDOSONIC units, which are third generation apex locator devices, were used to identify the root length in 58 teeth (82 roots). The electronic method was compared to radiographic and tactile sense methods. The results showed that APIT and ENDOSONIC devices were ineffective when used to determine the root canal length in 2–3 year-old dogs. A beep indicating the canal depth was heard in only two of 82 (2.4%) canals. The digital-tactile sense method with radiographic confirmation is more appropriate for root length measurement than the electronic method during endodontic therapy in dogs.