This invention relates to the novel selenium compounds which are useful as an antineoplastic agent. The compounds are represented by the general formula (I): wherein R, X, A and Y represent the groups specified below, a represents a number of 0 or 1, b represents a number of 0, 1 or 2, and (1) when a is 0 and b is also 0, c is 4, n is 1 or 2 and m is 0, (2) when a is 1 and b is 0, c is 2, n is 1 or 2 and m is 0 or 1, and (3) when b is 1 or 2, c, n and m are all 0; (i) when b is 2, R represents (1) a C.sub.4-10 alkoxy group substituted with a halogen atom, (2) a lower alkoxyl group substituted with a halogen atom and a phenyl group, or (3) a cycloalkyloxy group substituted with a halogen atom, and (ii) when b is 1, R represents a group represented by the formula ##STR1## (wherein R.sub.0 is a C.sub.2-6 alkyl group); X represents a halogen atom; A represents a compound represented by the formula ##STR2## (wherein R.sub.1 and R.sub.2 may be the same or different and represent a hydrogen atom, a hydroxyl group, a lower alkyl group, a halogen atom, a phenyl group, a cyano group, a lower alkoxycarbonly group, a phenoxycarbonyl group, an amino group (to which a lower alkyl, lower alkylaminocarbonyl, lower halogenoalkylaminocarbonyl or lower alkoxycarbonyl group may be bonded), a benzoyl group, a loweralkoxyl group, a carbamyl group or an allyloxycarbonyl group; R.sub.7 represents a hydrogen atom, a lower alkyl group or a group represented by the formula ##STR3## (wherein R.sub.9 represents an amino group or a lowr alkoxyl group); Y represents H.sub.2 O.
