To provide an impression material composition which has excellent tooth releasabiliy, excellent tray holdability and excellent operability, although containing a slightly water-soluble liquid compound for improving the property of the impression material in a relatively large amount.

This impression material composition is characterized by comprising (A) 100 pts. mass of an alginate, (B) 10 to 2,000 pts. mass, (C) 100 to 4,000 pts. mass of water, (D) 10 to 500 pts. mass of a slightly water-soluble liquid compound, (E) 1 to 100 pts. mass of an organic hydroxy compound satisfying the following expression (1) : (mol. wt.)÷(the number of hydroxyl groups) <40 (1), and (F) 0.4 to 4.1 pts. mass of an unsaturated carboxylic acid polymer. A polyhydric alcohol such as glycerol or a saccharide such as glucose is suitably used as the organic hydroxy compound of component (E), and poly(meth)acrylic acid or the like can also suitably be used as the unsaturated carboxylic acid polymer of component (F).