Abstract: The auto-synthesis method was developed for the on-line preparation of amyloid-beta (Aβ) plaques image agent ¹¹C-PIB. A intermediate, ¹¹CH₃OTf, made from ¹¹CH₃ which was produced from ¹¹CO₂ with LAH/THF, was bubbled into 1.0 mg precursor 6-OH-BTA-0 butanone solution in salt-ice condition. The final crude product was then purified though prep-HPLC to get purified product. The human images were obtained in four cases of AD and 1 normal volunteer. The total synthesis process took about 35 minutes. The synthesis yield (EOS) was (25±5)% (not correct), the radiochemical purity over 98%, and the specific activity about 5.55 GBq/μmol. The modified automated preparation of ¹¹C-PIB was verified in producing ¹¹C-PIB of high radiochemical purity and synthesis yield in a short time. The results showed that this promising product could be used in clinical imaging.