A sheet for thermoforming made of a polylactic acid resin composition containing a polylactic acid-based resin, a plasticizer, and a crystal nucleating agent, wherein the sheet has a thickness of from 0.1 to 1.5 mm, and wherein Re (cal) calculated by the following formula (A): Re (cal) = Re (obs)/d×10 -6 (A), wherein Re (obs) is a phase difference (nm) measured at a wavelength selected from wavelengths of from 380 to 780 mm, and d is a thickness (mm) of the sheet, is within the range of 0.001 × 10 -3 ‰¤ Re(cal) ‰¤ 1 × 10 -3 . The sheet for thermoforming of the present invention has a wide moldable temperature region, so that the sheet can be suitably used in various applications such as food containers, packaging materials for daily sundries and household electric appliances, industrial trays of industrial parts, and the like.