Isoamylase gene (iso) of Pseudomonas amyloderamosa was amplified by polymerase chain reaction and cloned into Saccharomyces cerevisiae vectors under the control of alcohol dehydrogenase gene and glyceraldehyde-3-phosphate dehydrogenase gene promoters. The signal sequence of iso gene was also replaced with that of Schwanniomyces occidentalis alpha-amylase gene. The extracellular isoamylase activity of transformed Sacc. cerevisiae could reach 86 U ml(-1) after a 4-days cultivation.