Real-time moisture monitoring of crystal powder in a pilot-scale fluidi-ed-bed dryer was examined in the conversion of lactulose trihydrate crystal powder into lactulose anhydride crystal powder. Two types of in-line near-infrared spectroscopy (NIRS) were investigated as means to estimate moisture content. Of these, a simplified filter type spectroscopy with 3 wavelengths showed poor accuracy in estimating moisture content, while a method using Fourier-transform spectroscopy showed high accuracy, notably when the moisture content less than 1.00%. This technique allowed real-time monitoring of the moisture content in the crystal powder and was applicable to automatic endpoint determination in the fluidi-ed-bed dryer.