The atmospheric pressure He- H 2 O plasma jet has been analyzed and its effects on the Kapton polyimide surface have been investigated in terms of discharge power effect. The polyimide surfaces before and after plasma treatment were characterized using atomic force microscopy (AFM), X-ray photoelectrons spectroscopy (XPS) and contact angle. The results showed that, increasing the discharge power induces remarkable changes on the emission intensity, rotational and vibrational temperatures of He- H 2 O plasma jet. At the low discharge power ≤5.2 W, the contact angle analysis of the polyimide surface remarkably decrease owing to the abundant hydrophilic polar C=O and N–C=O groups as well as increase of surface roughness. Yet, plasma treatment at high discharge power ≥5.2 W results in a slight decrease of the surface wettability together with a reduction in the surface roughness and polar groups concentrations.