External exposure to veterinary staff and pet owners from 18 F-fluorodeoxyglucose positron emission tomography ( 18 F-FDG, dose 170±33 MBq/head) in veterinary nuclear medicine was measured by monitoring the surface (SDR) and ambient dose rates (ADR) from animal patients (dogs and cats). The patientsʼ weights ranged from 4.2 to 32.3 kg (11±9.4 kg). The highest SDR was at the ventral abdomen, and its SDR time course was within the degradation curve with a physical half-life (109.8 min). ADR demonstrated a significant decrease up to approximately 30-to 80-fold by keeping a 100-cm distance from the patient. The estimated occupational radiation dose from the FDG injection before sedation was higher than the dose received from the FDG injection after general anesthesia. All patients showed acceptable SDRs, which was less than 3.8 µSv/h at 24 h post-injection, where cumulative SDR until infinity was less than 1/100 of the limit of the yearly external public exposure (1 mSv/year) which recommended in ICRP publication 103. According to the current legislation in Japan, these results represent an overregulation of detention 24 h after FDG injection in the case of an adequate lower maximum SDR.