Abstract: A method for the determination of 4-nonylphenol in rat serum was established by ultra-high performance liquid chromatography-tandem mass spectrometry(UPLC-MS/MS)to study the metabolic kinetics of 4-nonylphenol in female rats after gavage administration of low dose of 4-nonylphenol. The results showed that the matrix effects did not interfere with the determination of 4-nonylphenol. The method showed good linear relationship with 0.5~50.0 ng/mL(r=0.9950),the limit of detection for 0.09 ng/mL,the limit of quantitation for 0.3 ng/mL. The relative recoveries were 80.21%~104.23%. The intra- and inter-day relative standard deviations(RSD)were less than 10%,respectively. Metabolic kinetics studies showed that 4-nonylphenol conformed to the two-compartment model in rats,the peak concentration(C_max)of 24.34 ng/mL at 0.04 h,and the rate of transport from the peripheral compartment to the central compartment(k₂₁=0.38/h)was greater than the rate of transport from the central compartment to the peripheral compartment(k₁₂=0.23/h),the distribution phase half-life(t1/2α=1.12 h)was smaller than the elimination phase half-life(t_1/2β=84.99 h). The results indicated that 4-nonylphenol had the characteristics of fast absorption,fast distribution and low clearance rate in vivo.