TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Polyamino Acid: The polyamino is poly aspartic acid, poly glutamic acid, polylysine or polysuccinimide. The polyamino acid has cross linked structure in at least a part of its molecular structure.Preferred Amount: The content of polyamino acid in the promoter is 0.1-100 weight %. The promoter is added in quantity which corresponds to 0.001-100 weight parts (wt.pts) by polyamino acid conversion to 100 wt.pts of wet target substance to be decomposed.Preferred Properties: The biodegradation promoter has decomposition promotion degree (Lr) or (Ld) of 0.05-20. The target object is biodegraded by compost method, according to ISO14855, and degree of decomposition (Lr) is measured by assaying the generated carbon dioxide, or degree of decomposition (Ld) is obtained by measuring change in dry weight of decomposition target object. Lr is defined by the expression (Ga-Gd-Gn)/Wd, where Ga is the total weight of carbon dioxide produced from the whole target object which contains polyamino acid when the organic substance in decomposition object is decomposed, when polyamino acid is added; Gd is the total weight of carbon dioxide produced by the decomposition of the added polyamino acid; Wd is the weight of added polyamino acid; and Gn is the total weight of carbon dioxide produced by decomposition of the organic substance in the target object, when polyamino acid is not added. Ld is defined by the expression (Wn-Wa)/Wd, where Wa is the dry weight of decomposition target object which contains polyamino acid, after decomposition of the organic substance in the target object, when polyamino acid is added; Wd is the amount of polyamino acid added; and Wn is the dry weight of target object, obtained after decomposition of organic substance in the target object, when polyamino acid is not added.    TECHNOLOGY FOCUS - ENVIRONMENT - Preferred Method: The target object is decomposed in an artificially controlled environment. EXAMPLE - (In weight parts) 2% ethanol liquid (0.166) and 14C-aspartic acid (20) having radiation activity of 9.25 MBq were mixed with 85% phosphoric acid (10), and reacted for 4 hours at 200degreesC, 20 mmHg using rotating evaporator. The reaction mixture was dissolved in dimethyl formamide (100), and added to water (500) and filtered. The precipitate was washed with water until the wash water became neutral, and dried at 60degreesC, and 14C labeled polysuccinimide (14.1) having weight average molecular weight of 96,000 and radiation activity of 0.884 MBq/g was obtained. 14C labeled polysuccinimide having radiation activity of 3.5 MBq on target object (organic refuse in composed) showed decomposition promotion degree of 1.37, which revealed the favorable decomposition promotion effect of the 14C labeled polysuccinimide.