Abstract: To model laminated composite plate and shell structures, a 6-node co-rotational curved triangular composite shell element is proposed. It is different from other existing co-rotational element formulations in the following ways: 1) Additive vectorial rotational variables are employed in the present element, thus updating nodal rotational variables is quite simple in a nonlinear incremental solution procedure; 2) Symmetric tangent stiffness matrices are achieved in both the local and global coordinate systems owing to the commutativity of the nodal variables in calculating the second derivatives of strain energy with respect to the local nodal variables and, through chain differentiation, with respect to the global nodal variables; 3) A mixed formulation procedure is employed to overcome membrane and shear locking problems. Four composite shell problems with large deformations are solved, and the results are compared with those from other literature, through which the proposed element formulation demonstrates its reliability and computational efficiency.