A simple scaling analysis of protein solubility in semi-diluted polymer aqueous solutions was derived based on the recent theoretical development of Abbott et al.1 on the interactions between protein spheres and entangled polymer coils and the experimental observations of Atha and Ingham2 on the polymer-induced protein precipitation. Both the hard-sphere nature of the protein and the flexibility of the polymer coils have been taken into account in the model. The experimental data can be fitted by using this model with physically reasonable values of the exponent. This approach may be useful in estimating protein solubilities in water in the presence of polymer from limited and usually costly experimental data.