Disclosed are: a thickening-inhibiting agent for inhibiting thickening of the peritoneal membrane by which thickening of the peritoneal membrane can be inhibited, prevented or treated with relieved side effects； and a dialysis solution which contains this thickening-inhibiting agent. Specifically disclosed are: an agent for inhibiting thickening of the peritoneal membrane, which contains, as the active ingredient, a chromanol glycoside represented by chemical formula (1)； and a dialysis solution containing the same. In chemical formula (1), R1, R2, R3 and R4 are either the same or different and each represents a hydrogen atom or a lower alkyl group； R3 represents a hydrogen atom, a lower alkyl group or a lower acyl group； X represents a monosaccharide residue or an oligosaccharide residue, in which the hydrogen atom in a hydroxyl group in each saccharide residue may be substituted by a lower alkyl group or a lower acyl group； n is an integer of 0 to 6； and m is an integer of 1 to 6.
