Summary The golden hamster possesses a forestomach and a glandular stomach. The gastric groove connects the cardia to the glandular stomach and is situated on the lesser curvature of the stomach. The constitution of the muscle fibers in the gastric groove was investigated. The gastric groove consisted of two lips and a groove floor. The muscle coat of the lips was composed of a mixture of smooth and striated muscle fibers. The smooth muscle fibers were components of the cardiac muscle loop. The striated muscle fibers were extensions from the esophageal inner circular muscle layer, and invaded about half the length of the lips. The muscle coat of the groove floor consisted of an inner circular muscle layer made up of smooth muscle fibers, and the outer longitudinal muscle layer of the striated muscle fibers extended from the esophageal outer longitudinal muscle layer. The present study revealed that the muscle coat of the gastric groove in the golden hamster was composed of smooth and striated muscle fibers, and that these striated muscle fibers were extensions of the esophageal muscle coat.