Polyisobutenylsuccinic anhydride (PIBSA), an intermediate for the lubricating oil additive, was prepared by the reaction of polyisobutylene (PIB) with maleic anhydride (MA). The functionality, which indicates the extent of reaction of PIB-a and MA, was determined in the various reaction conditions : fuctionality was 0.98 under the reaction conditions of no solvent for 12 hours at 190℃, 0.21 in benzyl alcohol solvent for 12 hours at 190℃, and 0.03-0.20 with various Lewis acids such as AlCl_{3, SnCl4, Et2AlCl, and TiC14. The fuctionality also depended on the structure of PIBs. As α-olefin content(ego-form) in PIB increased, the fuctionality had a higher value. The structure of PIBSA prepared from PIB and MA was determined with FT IR spectroscopy. Two strong anhydride IR bands at 1782 and 1855 cm^-1 were obserbed. Polyisobutenylsccinimide (PIBSI), a lublicating oil additive, was prepared by the reaction of PBSA with diaminoethane.}