This invention relates to novel phosphonic acid esters represented by the following general formula (I) ##STR1## wherein R.sup.1 represents a lower alkyl group or an aryl group,R.sup.2 represents a lower alkyl group or a lower alkoxy-lower alkyl group,R.sup.3 represents a fluoro-substituted lower alkyl group,X represents an oxygen or sulfur atom,Y represents an oxygen or sulfur atom or a group of the formula ##STR2## in which R.sup.4 represents a hydrogen atom or a lower alkyl group, Z represents a hydrogen atom, a halogen atom or a lower alkyl group, andn represents 0 or 2,which can be used as insecticidal, miticidal and nematocidal agents.