question: Neonatal Fc receptor (FcRn) and beta-2 microglobulin (ß2M) play an important role in transporting maternal immunoglobulin G (IgG) to fetuses, maintaining the homeostasis of IgG and albumin in human body, and prolonging the half-life of IgG- or albumin-based biotherapeutics. Little is known about the influence of age, gender and race, and interindividual variability of human FcRn and ß2M on the protein level. In this study, an ultra-performance liquid chromatography (UPLC)-multiple reaction monitoring (MRM) mass spectrometry (MS)-based targeted quantitative proteomic method was developed and optimized for the quantification of human FcRn and ß2M. Among the 39 human livers studied (age 13 - 80 years), the mean ({plus minus} S.D.) concentrations of FcRn and ß2M were 147 ({plus minus} 39) and 1250 ({plus minus} 460) pmol/g of liver tissue, respectively. A four-fold interindividual variability (63 - 243 pmol/g of liver tissue) was observed for the hepatic FcRn concentration. A moderate correlation was found between the hepatic ß2M and FcRn expression levels. Influences of age, gender and race on the hepatic expression of FcRn and ß2M were evaluated. The findings from this study may aid the development of physiologically based pharmacokinetic models that incorporate empirical FcRn tissue concentrations and interindividual variabilities, and the development of personalized dosing of biopharmaceuticals. Significance Statement This is the first study to evaluate the influence of age, gender and race on the expression of FcRn and ß2M and their interindividual variability in human livers. This study describes a validated UPLC-MRM-based targeted quantitative proteomic method for quantifying human FcRn and ß2M in biological tissues. Results from this study may aid current development of PBPK models for biotherapeutics, where FcRn plays a significant role in clearance mechanism and its expression level and interindividual variability are largely unknown.