Huo Luo Xiao Ling Dan (HLXLD), a Chinese herbal formula composed of 11 different herbs, has been used traditionally for the treatment of arthritis and other chronic inflammatory diseases. However, the pharmacokinetic profile of its anti-inflammatory bioactive compounds has not been elucidated. Boswellic acids are the bioactive compounds with potent anti-inflammatory activity isolated from Boswellia serrate which is one of the 11 herbs of HLXLD. The objective of the study was to compare the pharmacokinetics of the two bioactive bowsellic acids: 11-keto-β-boswellic acid and 3-O-acetyl-11-keto-β-boswellic following oral administration of HLXLD or Boswellia serrata extract alone in normal and arthritic rats. An LC-MS method was developed and validated for the determination of 11-keto-β-boswellic acid and 3-O-acetyl-11-keto-β-boswellic in the comparative pharmacokinetic study. The results showed that there were significant differences in pharmacokinetic parameters between normal and arthritic groups. Interestingly, the absorptions of two boswellic acids were significantly higher in HLXLD than Boswellia serrata extract alone, indicating the synergistic effect of other herbal ingredients in HLXLD. This comparative pharmacokinetic study provided direct evidence supporting the notion that the efficacy of a complex mixture such as HLXLD is better than that of single components in treating human diseases.