The effect of temperature on vibrational frequency shifts in mechanically stressed polymer chains is analyzed. A single chain is modeled as a weakly coupled, one‐dimensional series of anharmonic diatomic oscillators. The anharmonic potential is described as a perturbation of the harmonic potential with cubic and quartic terms. Expressions are derived for the dominant, quasiharmonic contribution to the temperature‐dependent frequency shifting coefficient &agr;c, and distinctions are drawn between the vibrational mode ’’mixing contribution’’ and the ’’anharmonic contribution.’’ &agr;cis derived in terms of the Gru¨neisen parameter; and the resulting expression is −&agr;c= &agr;0+&bgr;0T, where &agr;0is the extrapolatedT= 0 °K value of the frequency shifting coefficient, and &bgr;0is constant. The predicted linear dependence of &agr;con temperature was found to be in excellent qualitative agreement with experimental studies on stress‐induced infrared frequency shifts versusTin polypropylene.