A specific phase structure was observed for binary blends of poly(isoprene)-block-poly(styrene)-block-poly(2-vinylpyridine) (ISP) triblock terpolymers with asymmetric chain lengths of two end-blocks. Tetragonal-packed cylinders were obtained from various binary blends on a wide range of volume fractions, although the sizes of I and P cylinders were highly asymmetric. Those structures have never been found for monodisperse ABC triblock terpolymers, and the three specific features have been confirmed: (1) I cylinders were metamorphosed into rod domains, and their interfaces have nonconstant mean curvatures; (2) the cross-sectional area ratio of I/P domain is qualitatively changed with the volume fraction of each component; and (3) spherical and cylindrical domains of P component coexist. The molecular design adopted in the present work, that is, I and P blocks in two parent terpolymers have both fairly large chain length difference, must lead to these new morphologies.