Abstract: To investigate the effect of ionic liquid based on choline and citronellic acid (Cho CA, COCA) on the oral absorption of poorly soluble drug cyclosporin A (CsA), COCA was synthesized using choline and citronellic acid by one-step neutralization method, and then characterized by mass spectrometry, ¹H-NMR, and infrared spectrophotometry. Next, CsA-ionic liquid (CsA-COCA) was prepared by ultrasonic-assisted method and filled into enteric-coated capsules. After oral administration of CsA-COCA capsules or CsA suspension preparation in rats, CsA concentration in whole blood was assayed using liquid chromatography-tandem mass spectrometry (LC-MS/MS) method, and the pharmacokinetic parameters were calculated by DAS 2.0 software. All animal care and experiments followed the approval of Institutional Animal Care and Use Committee at Peking University Health Science Center. The results indicated that compared with oral administration of 10 mg·kg^-1CsA suspension, the area under the curve (AUC), half-life time (T_1/2), and mean residence time (MRT) of CsA obtained by oral administration the same dose of CsA-COCA increased by 2.81, 4.41, and 1.77 times, respectively. The COCA prepared in this study can significantly promote the oral absorption of CsA in rats, and prolong the half-life. This study can provide reference for the study of oral formulation of insoluble drugs such as CsA.