NOVELTY - An esterase comprising amino acid sequence exhibiting homology to amino acid sequence of SEQ ID NO: 1, is new. The esterase has polyester decomposition activity. The esterase acts specifically with respect to medium chain fatty acid ester. The esterase has a molecular weight of 27.8 kDa.    USE - The esterase is useful for decomposing polyester, particularly biodegradable plastics chosen from poly( epsilon -caprolactone) and polyethylene terephthalate, and modifying polyester material. The method (M1) is useful for decomposing triacylglycerol. The method (M2) is useful for producing biodiesel (all claimed).    ADVANTAGE - The esterase has high thermal stability to 70 degrees C, high pH tolerance to 6.5-9.5 and high temperature tolerance to 30-70 degrees C.    DETAILED DESCRIPTION - An esterase comprising amino acid sequence exhibiting homology to amino acid sequence of SEQ ID NO: 1, is new. The esterase has polyester decomposition activity. The esterase acts specifically with respect to medium chain fatty acid ester. The esterase has a molecular weight of 27.8 kDa. Sequence not defined here may be found at ftp://ftp.wipo.int/pub/published_pct_sequences/publication. INDEPENDENT CLAIMS are included for the following:    (1) esterase gene comprising DNA chosen from (a) DNA capable of encoding esterase which comprises amino acid sequence of SEQ ID NO: 1 or 2, (b) DNA comprising base pair sequence of SEQ ID NO: 3 or 4, and (c) DNA capable of encoding esterase which comprises amino acid sequence exhibiting homology to amino acid sequence of SEQ ID NO: 3 or 4;    (2) recombinant DNA comprising the esterase gene;    (3) microorganisms comprising the recombinant DNA;    (4) enzyme agent utilizing the esterase as an active ingredient;    (5) method (M1) for decomposing triacylglycerol involves processing triacylglycerol using the esterase or enzyme agent; and    (6) method (M2) for producing biodiesel involves mixing fats, oils and alcohol by transesterification process using the esterase.