Part of a β-amylase genomic DNA sequence from the oomycete, Achlya bisexualis was cloned by polymerase chain reaction (PCR) using degenerate oligonucleotide primers derived from the conserved regions of other known β-amylase sequences. The 5′- and 3′-regions of the β-amylase gene were amplified by genome walking method. The Ach. bisexualis β-amylase gene consisted of a 1338bp open reading frame, encoding a protein of 446 amino acids with a molecular weight of 49 381Da, and was not interrupted by any intron. The deduced amino acid sequence of the β-amylase gene had 67% similarity to the β-amylase of Saprolegnia ferax, followed by 40% similarity to that of Arabidopsis thaliana. The β-amylase gene was expressed in Saccharomyces cerevisiae placing it under the control of the alcohol dehydrogenase gene (ADC1) promoter.