The invention provides an impression plastic tray for a lower jaw which is made of a plastic, can prevent a set impression material from floating upward from the tray and being peeled off from the tray, and can be used for taking an impression with high accuracy. The impression tray has an outer wall (2) and an inner wall (3) and a bottom portion (1) forming a flat U-shaped surface with an approximately uniform width. A rim (4) is provided along each of upper ends of the outer wall (2) and the inner wall (3). Elongate through holes (5) extend vertically from just below the rim (4) to the bottom portion (1) in the inner and outer wall. The distance between adjacent through holes is 2 to 5 times the width of said elongate through holes (5). Circular through holes (6) and elongated through holes (7) are provided in the bottom portion (1).
