Aging is a time-dependent process that causes metal bioavailability to decrease with time. The current study investigated the bioavailability change of Pb in four contrasting soils over a time period until the Pb relative bioavailability (RB) levels achieved a steady state to assess the extent of the following: firstly, bioavailability change in each soil and secondly, correlation of these changes with the soil properties. Relative bioavailability of soils spiked with 1500 mg Pb/kg were measured in swine that were fed these soils, throughout an aging period (56 days) to investigate relationships between soil properties and in vivo bioavailability of Pb. Spiked soils were used to minimize the effect of varying sources of Pb on RB. The RB of Pb in GTA, IWA, and MLA decreased from their initial Pb RB values until a steady state RB of 34, 45, and 59 % was reached, respectively, by the 56th day. In contrast, however, to these RB decreases, NTA soil indicated no change in RB over the whole aging period of the experiment. The lack of change in RB in the NTA soil over time was attributed to it achieving a steady state RB within a very short time due to its comparatively high sorptive capacity (K d = 112).