Previously we reported the anticonvulsant activity of an initial series of N-1',N'-3' disubstituted-spiro-phthalidyl hydantoins that were prepared by reaction of the corresponding N-1',N'-3'-disubstituted ureas with ninhydrin, followed by treatment with aqueous sodium periodate oxidation. The new class of spirohydantoins exhibited anticonvulsant activitites in both the maximal electro shock (MES) and pentylene tetrazole (PTZ) tests. While N-1'-aryl substituted hydantoins showed appreciable anticonvulsant activities in PTZ assay, they exhibited less in the MES test. With increase in chain length there is increase protection against PTZ induced convulsions. In the rotarod test, compounds bearing straight alkyl chain at the para position of N-1'-aryl group were less neurotoxic than the branched groups like t-butyl at the para position. Also change in position of the substituent from para to ortho does not greatly affect the anticonvulsant activity. Results of these latest tests will be discussed in terms of ED50's and structure activity relationships for its anticonvulsant activity.