The effects of physical aging on the mechanical and thermal behavior of a high performance engineering resin, poly(arylene etherimide) (PEI), were characterized as a function of aging time and temperature using dynamic mechanical spectrometry (dms), room temperature tensile tests, and differential scanning calorimetry (dsc). The aging temperature range investigated extended fromTg−140 °C toTg−20 °C. dms and tensile measurements demonstrated that aging for 1000 and 10 000 min at temperatures as low asTg‐140 °C had a significant influence on the mechanical behavior of PEI. Shift rates (μ), as defined by isothermal increases in the dynamic storage modulus (E’) as a function of frequency, ranged from 0.4 to 3.0 with increasing aging temperature. Dynamic loss modulus measurements (E‘) demonstrated that PEI has a pronounced β relaxation which exhibits a significant decrease in magnitude with aging. Suppression of this relaxation paralleled dramatic changes in the room temperature stress‐elongation behavior of PEI. Increases in yield strength after aging for 10 000 min were as large as 16%, while elongations at break decreased by as much as 64%. While mechanical measurements demonstrated aging effects for all temperatures studied, changes in thermodynamic behavior by dsc, occurred only after aging at temperatures greater thanTg−55 °C.