The novel bisphosphonic acid ester derivatives represented by the following formula (1):Y—Cy—(NH)m—(CH2)n—C(X)(PO(OR1)(OR2))2 (1)wherein each symbol is as defined in the DESCRIPTION, which has an amino group substituted by a heterocyclic group or a heterocyclic group containing a nitrogen atom, and the acid moiety is esterified with a POM group, an n-butanoyloxymethyl (BuOM) group and the like, exhibit a superior direct or indirect cytotoxicity effect on tumor cells and virus infected cells.
