The objective of this study was to investigate a new protein with alpha-glucosidase inhibitory activity from the rhizomes of Zingiber ottensii. With a simple salting-out technique followed by single-step anion-exchange purification, the protein was successfully purified from the rhizomes. This protein was found to have three likely sub-unit types, 32.5, 15.2, and 13.8 kDa, as revealed by native and reducing SDS-PAGE analysis. Determination of the kinetics of the inhibition of alpha-glucosidase from Saccharomyces cerevisiae by standard enzymatic methods indicated the maximum percent inhibition; IC50 and K (i) of this protein were 77.5%, 30.15 mu g/ml, and 140 mu mol, while the K (m) and V (max) were 2.35 mu mol and 0.11 mM/min, respectively. The inhibitory action was pH-independent within the pH range 2-10, but was potentially affected by buffer salts, and was relatively temperature-stable between 4-35 A degrees C, with a maximum activity at 65 A degrees C. The amino acid sequence of an internal fragment of this purified Z. ottensii rhizomal protein had a similarity to the sequence from the plant cysteine proteinase family. Although this alpha-glucosidase inhibitory protein was purified from Z. ottensii rhizomes and preliminarily characterized, further studies are needed prior to firm applications being envisaged.