Peripheral nerve injury (PNI) is a complex clinical challenge affecting quality of life. Neurological recovery does not always ensure functional recovery as extracellular matrix (ECM) alterations affecting muscle function. This study evaluates hyaluronan (HA) and collagen concentration in gastrocnemius muscle and thoracolumbar fascia (TLF) in unilateral lower limb PNI rats to ex-plore systemic ECM alterations following PNI and their impacts on functional recovery. Eighteen 8-week-old male Sprague-Dawley rats were divided into experimental (n=12 with left sciatic nerve transection injury repaired by nerve conduit) and control (n=6) groups. After six weeks, motor function was evaluated. Muscle and TLF samples were analyzed for HA and collagen concentrations using Purple-Jelley HA Assay and Total-Collagen Assay kit. HA and collagen distribution was assessed using Alcian Blue and immunohistochemistry, and Picrosirius Red staining. In PNI rats, SFI and gait analysis were -87±9.12 and 1.32±0.29. Both sides of muscles showed significantly lower HA concentration than that in healthy rats (left p