The Grignard reactions of 1-phthalazine-(V-0), 2-quinoxaline (VI-0), and 4-cinnolinecarbonitrile (VII-0) were carried out. Grignard reagent used in this study was as follows ; phenylmagnesium bromide, benzylmagnesium chloride, isopropylmagnesium bromide, ethylmagnesium bromide, and methylmagnesium iodide. When a mixture of V-0 and Grignard reagent in tetrahydrofuran (THF) was refluxed for 3 hr, 1-alkylphthalazine (Va), 4-alkyl-3, 4-dihydro-1-phthalazinecarbonitrile (Vc), 4-alkyl-1-phthalazinecarbonitrile (Vc'), 2-alkyl-1(2H)-phthalazinone (Vd), and 4-alkyl-3, 4-dihydro-3-(1-phthalazinyl)-1-phthalazinecarbonitrile (Ve) were formed together with 1-benzoylphthalazine (Vb-1), 1, 4-diethyl-phthalazine (Vf-4), 1, 2-dihydro-1, 1, 2-triethyl-phthalazine (Vg-4), and 3, 4-dimethyl-3, 4-dihydro-1-phthalazinecarbonitrile (Vh-5), although the yields of all products were small. The reaction of VI-0 in THF carried out under the same conditions as V-0 gave 2-alkylquinoxaline (VIa), 2-acylquinoxaline (VI-b), 3-alkyl-3, 4-dihydro-2-quinoxalinecarbonitrile (VIc), 3-alkyl-2-quinoxalinecarbonitrile (VIc'), and 1-alkyl-2 (1H)-quinoxalinone (VId) together with 2, 2' : 3', 2-terquinoxaline (VIi), in very small yields. The reaction of VII-0 with phenylmagnesium bromide and methylmagnesium iodide in benzene gave only d type of the compound (1-phenyl-(VIId-1), and 1-methyl-4 (1H)-cinnolinone (VIId-5)), and did not isolate other type of the compound. These, a, b, and c type of the compounds were expected reaction products, and other, c', d, e, f, g, and h type of the compounds were unexpected products. Especially, e type of the compound was the product peculiar to the Grignard reaction of V-0, and d type of the compound was characteristic product of the Grignard reactions of the cyanobenzodiazines except 4-quinazolinecarbonitrile (IV-0) giving only a type of the compound. The possible mechanisms of the formations of a, b, c, c', d, and e type of the compounds were proposed.