PROBLEM TO BE SOLVED: To obtain a liquid fertilizer for hydroponics capable of improving the yield of crops or quality thereof in the hydroponics. SOLUTION: This liquid fertilizer for the hydroponics is obtained by compounding at least one selected from a 2-11C carboxylic acid and its salt in an amount of 0.0001-0.03 wt.% based on a liquid fertilizer prepared by dissolving and/or dispersing a nitrogenous fertilizer, a phosphatic fertilizer and a potassium-based fertilizer in water with the liquid fertilizer.