There is some evidence that the handheld rectal thermometer does not accurately measure core temperature in bears. The objective of this study was to compare body temperature measured by the handheld digital thermometer (HDT), deep rectally inserted core temperature capsules (CTCs), and gastrically inserted CTCs in anesthetized brown bears (Ursus arctos). Twenty-two brown bears were immobilized with a combination of zolazepam-tiletamine and xylazine or medetomidine. After immobilization, one CTC was inserted 15 cm deep into the animal's rectum (DRTC) with a standard applicator, and another CTC was inserted into the stomach (GTC) via a gastric tube inserted orally. Temperature was measured every 5–10 min with an HDT. Paired temperature data points were analyzed with the Bland–Altman technique for repeated measurements and regression analysis with a significance level of 0.05. The mean difference ± SD of the difference between HDT and GTC readings was 0.27 ± 0.47°C and the 95% limits of agreement (LoA) were 1.20 and −0.66°C. The determination coefficient (r²) found between these methods was 0.68 (P < 0.0001). The mean difference ± SD of the difference between HDT and DRTC readings was 0.36 ± 0.32°C and the 95% LoA were 1.0 and −0.28°C. The r² between HDT and DRTC was 0.83 (P < 0.0001). The mean difference ± SD of the difference between the two insertions of the VitalSense® capsules was −0.06 ± 0.24°C and the 95% LoA were 0.42 and −0.54°C. The r² found between GTC and DRTC was 0.91 (P < 0.0001). This study demonstrates that DRTC provided accurate measurement of core temperature and that HDT did not accurately measure core temperature, compared with GTC in anesthetized brown bears.