The aim of this study was to investigate the anti-hygroscopic effect of I-leucine on the spray-dried powders of three Chinese herbal extracts, namely, Shuang-Huang-Lian (SHL), Mulberry leaves (ML) and Lucid Ganoderma (LG). The anti-hygroscopic effects were evaluated in terms of the ability to reduce the adherence to the spray-dryer, to increase the spray-drying yield, to enhance the flowability, to achieve anti-caking effect and to maintain the particle shape and the integrity against moisture stress. The results showed that the presence of leucine conferred to anti-hygroscopic effects on spray-dried SHL powders in a dose dependent manner. When the content of leucine was added to 10% (w/w) of spray-dried SHL, anti-hygroscopic effects appeared to reach a plateau with an increase in leucine content to 20% not leading to further significant improvement. In addition, the presence of 10% leucine to either ML or LG extracts also resulted in a similar anti-hygroscopic effect. The anti-hygroscopic effect conferred by leucine may be attributed to the enrichment of the excipient on the surface layer, which was indicated by the X-ray photoelectron spectroscopy, rather than the elevated glass transition temperature. The present study demonstrated that the addition of leucine in the feed solution may be a convenient means to achieve the anti-hygroscopicity of spray-dried herbal extract powders. (C) 2014 Elsevier B.V. All rights reserved.