Poly(trimethylene terephthalate) (PTT) and poly(ethylene terephthalate) (PET) warp knitted fabrics were treated by helium atmospheric pressure glow discharge plasma. Weight loss (%) measurements and scanning electron microscopy (SEM) analysis showed removal of lubricant and contamination by plasma etching effect. X-ray photoelectron spectroscopy (XPS) analysis revealed that surface oxidation resulted in formation of hydrophilic groups which enhanced moisture regain (%), after storage. Plasma treatments caused PTT to have more profound surface oxidation and cleaning effect. It was found that low-stress mechanical properties, evaluated by Kawabata evaluation system (KES-FB), were enhanced by plasma treatment. Surface property changes by plasma etching played important roles in changing not only low-stress mechanical properties but also bulk properties of both fabrics, as a result of changes in interfiber and interyarn friction.