Abstract: The present invention is a process for producing 3-methyl-2-oxoindoline as defined by the following chemical formula (2), including heating of propionylphenylhydrazide as defined by the following chemical formula (1) in the presence of at least one kind of basic calcium compound, characterized in that an organic solvent withstanding at least at a temperature of 180° C. in the presence of the basic calcium compound is employed by at least an amount of equal weight to that of the propionylphenylhydrazide. With the construction mentioned above, even when the amount of calcium oxide is reduced down to as little as 15% of a conventionally used amount, at least 75% of a corresponding yield attained conventionally has been achieved.