Recombinant spider silk proteins, such as eADF4(C16), can be used for various applications. Colloidal particles of eADF4(C16) show potential as drug delivery systems. Tuning the colloidal properties of suspensions of eADF4(C16) particles represents a major prerequisite for their use in pharmaceutical formulations. In this study we determined the surface properties concerning inter-particle interactions by means of electrophoretic mobility and direct force measurements. The surface charge of eADF4(C16) spider silk particles was determined as a function of ionic strength and pH, respectively. The resulting electrophoretic mobility can be described using the O'Brien and White theory and is directly related to the amino acid sequence of the protein. We determined the extension of a fuzzy protein layer protruding into the solution by direct force measurements using a colloidal probe technique. This soft layer leads to deviations in the electrophoretic mobility and is responsible for additional repulsive forces at small separation distances. These steric forces lead to a stabilization of the particle suspension at high ionic strength.