In this study, silica particles were used to improve target protein batch crystallisation from a binary protein mixture at a 5 mL scale. Lysozyme (40 mg mL−1) was used as the target protein and thaumatin (0.1–8 mg mL−1) was regarded as a protein impurity. It was demonstrated that even an impurity at the concentration as low as 0.1 mg mL−1 (0.25 w/w% of the target protein) would delay target protein crystallisation, predominantly by extending the induction time. When the silica particles were employed in the system to facilitate crystallisation, target protein crystallisation was significantly improved with a much shorter induction time and higher yield at the end of the experiment. It was also shown that the effectiveness of silica on target protein crystallisation depended on the impurity concentration and silica loading amount.