Myosin and its fragments, rod and subfragment-1 (S1), were prepared from the requiem shark Triakis scyllia and examined for the effects of urea on their α-helical structure by monitoring with circular dichroism (CD) using corresponding proteins prepared from the carp Cyprinus carpio as references. All of the protein preparations from requiem shark showed decreased α-helical contents with increasing urea concentrations. However, rod was most stable against urea treatment, whereas myosin and S1 exhibited similar patterns in urea concentration-dependent decrease of α-helix. When compared with the above results for requiem shark, proteins prepared from carp were less stable in terms of α-helical structure at least up to 2 M urea examined in the present study, irrespective of myosin and its fragments. Furthermore, α-helical structure of myosin, rod and S1 from requiem shark were completely refolded when urea was removed from the sample solutions. On the other hand, the refolding of α-helix in carp proteins after urea treatment was not perfectly accomplished, especially in the case of myosin and S1. Taken together, it is concluded that the α-helical structure of requiem shark myosin is highly resistant to urea denaturation.