A reversed phase high performance liquid chromatographic(RP-HPLC ) method for the simultaneous determination of rhynchophylline and isorhynchophylline in Uncaria Rhynchophylla was established by using ionic liquids as a mobile phase additive.With degree of separation and other related chromatographic parameters as indicators,the length of alkyl chain length and the type of anion in ionic liquid were selected.In addition,several influence factors,including imidazolium cation alkyl chain of ioinic liquids and concentration,mobile phase pH value and flow phase ratio were investigated.The probable mechanism of the separation with ionic liquids as mobile phase additives was also explored.The results showed that the longer the alkyl chain length of the cationic,the higher the separation efficiency of the anion,and the better the separation effect,that means the［HMIM］［BF4］ is the optimal mobile phase additive.The experimental results showed that when the ［HMIM］［BF4］ concentration is 16 mmol/L,the pH value of mobile phase is 3.0,and methanol ratio is 37%,baseline separations of rhynchophylline and isorhynchophylline were obtained, which could satisfy the requirements of sample separation.