Poly(ethylene)glycol (PEG)-based hydrogels are often used as matrix material for cell culturing. An efficient method to prepare soft PEG gels is by cross-linking via copper-free strain-promoted azide-alkyne cycloaddition (SPAAC). Here, the effect of polymer density and RGDS-content on hydrogel formation and cell adhesion was studied, by varying the total polymer content (10, 20 and 30 mg · mL-1) and the amount of RGDS moieties (0-100%) independently of each other. Rheology studies confirmed the soft nature of the hydrogels (G′ = 25-2 298 Pa). HOS cells are able to adhere well to all RGDS-containing gels. Interestingly, both HeLa cells and NIH 3T3 fibroblasts showed substantial adherence to 10 and 20 mg · mL-1 gels, but with increased hydrogel stiffness (30 mg · mL-1), their cellular adhesion decreased significantly.