Thermal conductivity enhancement by phonon inelastic scattering in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>Si</mml:mi> <mml:mrow> <mml:mn>1</mml:mn> <mml:mo>−</mml:mo> <mml:mi>x</mml:mi> </mml:mrow> </m

SiGe nanowires (NWs) exhibit significant potential for thermoelectric applications due to their tunable thermal transport properties. Through systematic investigation of ${\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}$ ($x=1%\ensuremath{-}50%$), we reveal a dual role of inelastic scattering in thermal transport that depends critically on Ge concentration. At low Ge concentrations (e.g., 1%), inelastic scattering reduces thermal conductivity by 25% through conventional phonon mean free path reduction, consistent with classical phonon scattering theory. Surprisingly, at higher Ge concentrations (e.g., 50%), we observe an anomalous 61% enhancement in thermal conductivity for NWs of 543.1 nm in length by inelastic scattering. This counterintuitive behavior arises from the interplay between diffusive transport and Anderson localization. Detailed transmission and characteristic length analyses reveal that inelastic scattering partially disrupts the phase coherence of phonons, leading to an increase in localization length and a enhancement of thermal transport within specific frequency regions. These findings fundamentally advance our understanding of phonon transport in disordered nanostructures and provide guiding principles for the design of materials with tailored thermal properties in thermoelectric materials and nanoscale devices.