Shear-induced phase separation was found in "nonentangled" oligomer mixture. The sheared mixture in one phase becomes turbid and its scattering pattern exhibits so-called "butterfly pattern" which is commonly observed in shear-induced phase separation of semidilute polymer solutions. The origin of the shear-induced phase separation is found to be dynamical asymmetry due to the difference in the glass transition temperature. (C) 2004 American Institute of Physics.