Collagen gels were modified by addition of co-gelling proteins to obtain gels with new functionalities. Microstructure and rheology of these mixed telopeptide-poor collagen gels were assessed. It was assumed that proteins with a low molecular weight strengthen the collagen structure by embedding themselves in the matrix, while high molecular weight proteins weaken the structure by interfering with the assembly of the network.Different combinations of collagen (2.8-5.19% (w/w)) and co-gelling protein concentrations (0.36-2.14% (w/w)) were applied. Blood plasma protein, soy protein isolate, whey protein isolate, and gluten were used as co-gelling proteins. The storage modulus was measured as an indicator of the gel strength. Frequency sweeps (0.1-10Hz) at 1% strain were conducted in the linear viscoelastic region. The position of the co-gelling proteins in the collagen matrix was examined via both confocal laser scanning and scanning electron microscopy.The results showed weakening effects for whey protein isolate. The addition of blood plasma protein did not affect the rheology, but the microstructure was influenced, featuring more fibrillar structures in the pores compared to the reference gels. Gluten seemed to lead to phase separation, forming a separate layer without interacting with the collagen matrix. The greatest impact was found for soy protein isolate, with a strengthening effect indicated by increased storage moduli and well distributed and embedded soy protein isolate in the collagen network.In conclusion, co-gelling proteins display a suitable approach to modify collagen strength in order to create matrices with new functionalities, such as co-extruded sausage casings with modified knack or snap.