The paper presents results of the study on the rheology modifiers of ceramic slurries used in the investment casting. The ceramic slurries used in the study were based on aluminum oxide powder in silica sol binder. Following modifiers were used as thickening agents: mpj, locust bean and xanthan gums. The influence of the substances on the slurry viscosity were tested with a silica sol binder before application to the ceramic slurries. The viscosity measurements were carried out with the use of ARES and Brookfield rheometres. The results obtained demonstrate the potential of employing the investigated substances as rheology modifiers for ceramic slurries used in the investment casting.