The water-powder ratio for gypsum-bonded investment influences the setting expansion. In this study, the effect of shaking off water drops on mechanical spatulator and hand spatula were investigated. The amount of water drops was measured by using an electronic balance. The total amount of water drops on the mixing set decreased very much after two times shaking off. By two times shaking off water drops, the influence on the setting expansion ratio of water drops can be avoided at the worst condition. The results demonstrated that shaking off water drops was effective for the setting expansion of gypsum-bonded investment.