Absorption heat pump systems (AHP) are an attractive technology to upgrade and utilize low temperature exhaust heat for refrigeration or heating-up without emitting global warming gases. This work proposes a method for forming a fine-particle slurry of LiBr crystals and evaluates the particle size distribution and effectiveness of the slurry for advancement of the vapor absorption performance in LiBr/water AHP. It was found that the fine-particle slurry of LiBr crystals is formed stably in solution under super-saturation conditions and the median diameter is correlated linearly with the mass ratio of crystal to zeolite in the slurry when zeolite powder is suspended. This phenomenon can be caused by the crystal growth around the zeolite particles, which function as nuclei. However, the deviation from this correlation becomes significant for ratios greater than 1.4 kg-LiBr/kg-zeolite and remarkable crystal growth is caused, such that size measurement is not possible beyond 2 kg-LiBr/kg-zeolite. The lab-scale vapor absorption examination revealed that the slurry improves the absorption rate by up to twice that of the homogeneous solution with 60% in LiBr concentration due to dissolution of the crystal, even if the solution is diluted by the absorption of water vapor in the absorber.