Abstract: A laminate of composite material with equilateral triangular patten of ribs is concetned.The ribs are equal in width and depth.The skin is braided to (0,±60)configuration.It behaves in a gross sense as a transversely isotropic material.The extentional and flexural stiffness matrix,the transverse shear stiffness and its coefficient of modification for this laminate aie devised.For a circular cylindrical shell manufactured by this laminate,design analysis in general instability is discussed and a simple formula for buckling is obtained.Numerical results agree well with experimental data.Computational example shows that the effect of the transverse shear deformation on the critical load is not significant.