PROBLEM TO BE SOLVED: To provide a method for improving saccharification efficiency of a plant, the plant to be used in the method, a method for producing biomass ethanol by using the plant, and a method for evaluating saccharification easiness of the plant.SOLUTION: The method for improving saccharification efficiency of a plant comprises applying saccharification treatment to a plant having functional deficiency mutation in at least one kind of lignin biosynthesis-related gene and having higher ratio of acid-soluble lignin content to Klason lignin content ([acid-soluble lignin content]/[Klason lignin content]) in the plant is higher than the ratio in a plant free from the functional deficiency mutation. There is further provided the plant wherein, in the genome in at least one cell constituting the plant, the CAD gene is a mutant, where the third cysteine from N-terminal side among four cysteine residues coordinated to structural zinc atom in CAD, is substituted with other amino acid.
