Rifaximin, a virtually non-absorbed rifamycin drug is gaining attention for its broad-spectrum of activity. A couple of methods have been reported for its determination in biological matrices. However, inconvenient sample preparation procedure, lack of sensitivity and long analysis time hindered the application of those methods in pharmacokinetic and toxicological study. Thus, a high performance liquid chromatography method has been developed and validated in this study for the sensitive quantification of rifaximin in serum. In this procedure, chromatographic separation was achieved by flowing a mobile phase comprise of acetonitrile and 0.1 % acetic acid (60:40, v/v) through a C18 column (150×4.6 mm, 5 μm). An ultraviolet detector was utilized to identify and quantify the compound. The method has been validated over a concentration range of 0.03-30.00 μg/ml (r2=0.9999) by utilizing 150 μl of serum. The accuracy of the method was 89.59-98.84 %, and the intra- and inter-day precisions were 0.41-6.84 and 1.83-5.71 %, respectively. The compound was stable in different storage conditions. Insignificant amounts (2.40±0.38 to 4.22±1.10 μg/ml) of rifaximin were quantified in serum samples of rat from 2 to 8 h after oral administration. This method offers a rapid, sensitive, specific, reproducible, and stable tool for the quantitative determination of rifaximin in serum, which could be applicable in other biological matrices and species for pharmacokinetic and toxicological study of rifaximin.