To provide a stable aqueous liquid agent containing (R)-(-)-5-(4-methoxy-3-propoxyphenyl)-5-methyl-2-oxazolidinone or a pharmacologically acceptable salt thereof in an effective concentration.

The aqueous liquid agent contains (R)-(-)-5-(4-methoxy-3-propoxyphenyl)-5-methyl-2-oxazolidinone or a pharmacologically acceptable salt thereof and hydroxypropyl-β-cyclodextrin. The method for solubilizing and stabilizing (R)-(-)-5-(4-methoxy-3-propoxyphenyl)-5-methyl-2-oxazolidinone and the pharmacologically acceptable salt thereof comprises incorporating hydroxypropyl-β-cyclodextrin with (R)-(-)-5-(4-methoxy-3-propoxyphenyl)-5-methyl-2-oxazolidinone or the pharmacologically acceptable salt thereof.