In the present study a new Mannich base 2-(dimethylaminomethyl)isoindoline-1,3-dione and its metal complexes with cobalt(II) and nickel(II) ions have been synthesized and characterized. Their structures have been established on the basis of analytical, magnetic, conductance and spectral data. 2-(Dimethylaminomethyl)-isoindoline-1,3-dione is found to act as a neutral bidentate ligand coordinating to the metal ion through a carbonyl oxygen and tertiary amino nitrogen atoms. The non-electrolytic natures of the complexes are evidenced by their molar conductance values. On the basis of magnetic moments and electronic spectral data, the CoII, NiII complexes are assigned a tetrahedral stereochemistry and the NiII complexes are assigned / octahedral geometry. The antimicrobial activity of the ligand and its complexes has been studied by agar-well diffusion method. Both the organic ligand and the complexes possess significant antimicrobial activity comparable to that of the standard drugs.