The present invention relates to a composition for noxious organisms-controlling agent having a synergistic effect and a method for using said composition, which comprises, as active ingredients thereof, one or more compounds selected from the phthalamide derivatives represented by general formula (I) being useful as an insecticide or acaricide and one or more compounds selected from the compounds having insecticidal, acaricidal or nematocidal activity: ##STR00001## wherein R.sup.1, R.sup.2 and R.sup.3 may be the same or different and each represent hydrogen atom, C.sub.3-C.sub.6 cycloalkyl, -A.sup.1-Qp, etc., each of X and Y may be the same or different and represents hydrogen atom, halogen atom, etc., n is an integer of 1 to 4, m is an integer of 1 to 5, and each of Z.sub.1 and Z.sub.2 represents O or S.