In a no-insulation (NI) REBCO magnet, the turn-to-turn contact resistivity ( c ) determines its quench selfprotection capability, charging delay time and the energy loss during field ramps. Therefore it is critically important to be able to control a range of c values suitable for various NI magnet coils. We used a commercial oxidizing agent Ebonol C to treat the copper surface of REBCO tapes. The copper oxide layer was characterized by cross-sectional transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS). The oxide layer formed in Ebonol C at 98 °C for 1 min is Cu 2 O of about 0.5 m. The c between two oxidized REBCO is in the order of 35 m-cm 2 at 4.2 K which decreases slowly with contact pressure cycles. The c increases but only slightly at 77 K. We also investigated the effect of oxidation of stainless steel co-wind tape on c . The native oxides on 316 stainless steel tape as well as those heated in air at 200 -600 °C were examined by TEM and XPS. The native oxides layer is about 3 nm thick. After heating at 300 °C for 8 min and 600 °C for 1 min, its thickness increases to about 10 and 30 nm respectively.For the stainless steel tapes with about 10 nm surface oxides, pressure cycling for 30,000 cycles decreases c by almost 4 orders of magnitude. Whereas at 77 K, it only changes slightly. For a surface with 30 nm oxide, the c decreases moderately with load cycles. The results suggest that for an oxidized stainless steel to achieve stable c over large number of load cycles a relatively thick oxide film is needed.