Oligo(ethylene glycol) (O‐EG_n)‐terminated alkanethiol surface‐assembled monolayers (SAMs) have been reported to demonstrate protein‐resistant properties similar to those of poly(ethylene glycol) (PEG). In this study, we compared the relative protein resistance of short and long ethylene oxide chains, SAMs of PEG 5000, PEG 2000, O‐EG₃ (molecular weight = 120), and O‐EG₆ (molecular weight = 240), on gold surfaces. Surface plasmon resonance showed that these monolayers were all protein‐resistant within the uncertainty of the measurement. However, they exhibited different adhesive properties toward 3T3 mouse fibroblast adhesion in supplemented Dulbecco's modified Eagles medium. The results show that the cell adhesion was sensitive to the concentration of proteins supplemented in the culture medium and to the length of PEG chains. © 2001 John Wiley & Sons, Inc. J Biomed Mater Res 56: 406–416, 2001