A novel monomethyl malonate derivative is represented by following Formula (I): ##STR00001## wherein X is a halogen atom; and Me is methyl group. This compound can be prepared by the steps of (A) reacting a benzyl halide derivative represented by following Formula (II): ##STR00002## wherein X and Y may be the same as or different from each other and are each a halogen atom, with dimethyl malonate in the presence of a base to yield a dimethyl malonate derivative represented by following Formula (III): ##STR00003## wherein X and Me have the same meanings as defined above; and (B) hydrolyzing the dimethyl malonate derivative of Formula (III). The compound is useful in the production of an indanonecarboxylic acid ester having a halogen atom on the indanone ring.