Context: The quadratus lumborum (QL) is expected to contribute to segmental motor control of the lumbar spine to prevent low back pain. It has different layers (anterior [QL-a] and posterior [QL-p] layers), whose functional differences are becoming apparent. However, the difference between the QL-a and QL-p activities during bridge exercises utilized in rehabilitation is unclear. Objective: To compare QL-a and QL-p activities during bridge exercises. Design: Repeated-measurement design was used to assess electromyographic activity of trunk muscles recorded during 14 types of bridge exercises. Setting: University laboratory. Participants: A total of 13 healthy men with no history of lumbar spine disorders participated. Intervention: The participants performed 14 types of bridge exercises (3, 3, and 8 types of side bridge, back bridge, and front bridge [FB], respectively). Main Outcome Measures: Fine-wire electromyography was used for QL-a and QL-p activity measurements during bridge exercises. Results: Both QL-a and QL-p showed the highest activity during the side bridge with hip abduction (47.3% [29.5%] and 43.0% [32.9%] maximal voluntary isometric contraction, respectively). The activity of the QL-a was significantly higher than that of the QL-p during back bridge with ipsilateral leg lift and FB elbow–toe with ipsilateral arm and contralateral leg lift (P < .05). With regard to the QL-p, the activity of the FB hand–knee with contralateral arm and ipsilateral leg lift, the FB elbow–knee with contralateral arm and ipsilateral leg lift, and the FB elbow–toe with contralateral arm and ipsilateral leg lift were significantly higher than that of the FB elbow–knee and FB elbow–toe (P < .05). Conclusion: This study indicates different regional activities; the QL-a activated during the back bridge with ipsilateral leg lift and FB with ipsilateral arm lift, and the QL-p activated during the FB with ipsilateral leg lift. These results have implications for the rehabilitation of low back pain or lumbar scoliosis patients based on QL recruitment.