Anatomical variations of the flexor digitorum superficialis (FDS) muscle are uncommon and is related to evolution of muscle from amphibians to human. These variations are of academic interest and should be considered when facing variations in clinical examination, interpreting radiological images and in surgical procedures such as tendon graft.We report a case of unilateral variation of FDS muscle in the forearm with two muscle bellies: superficial and deep which has not been reported before. The humeroulnar and radial origins of the superficial belly united to form a single muscle belly, which divided in the upper part of forearm into two tendons, that passed through carpal tunnel and inserted into the middle phalanges of third and fourth digits.The deep belly originated from medial epicondyle of the humerus next to flexor carpi ulnaris, continued as a short tendon in the upper part of forearm and then formed a second muscle belly in the middle third of the forearm (two muscle bellies separated by an intermediate tendon). In the lower part of forearm deep muscle belly divided into two tendons which traversed the carpal tunnel and was inserted into middle phalanx of second and fifth digits.The report enhances the knowledge on variation of FDS and add a note to understand atypical findings on physical examination and during surgery.