Spray freeze-drying (SFD) is a comparatively new method of producing biopharmaceutical powder preparations. In this study, Lactobacillus casei (IFO 15883) was spray freeze-dried to obtain a fine probiotic powder. The survival rate of L. casei in the powder after the SFD process was measured using plate agar counting. To improve the survival rate of L. casei during the SFD process, various experimental conditions were carried out. Among five growth media compositions, in Lactobacilli MRS broth with 1% mannose and 0.1% CaCO3, the viability of the freeze-dried powder was not significantly different from that of the initial powder (p >0.05). The most effective air pressure and protective agent during SFD were 20 kPa and buffered peptone water (BPW), respectively. Scanning electron microscopy (SEM) was applied to estimate the physical structure and properties of the particles. SFD probiotic particles were of various shapes and sizes with porous structures under different SED conditions. The average diameter of optimized probiotic powder particles with annealing was 24.8 mu m. The survival rate of the final SFD probiotic powder under conditions was 97.7%. (C) 2014 Elsevier Ltd. All rights reserved.