Small-sized composting experiment shows that the C/N ratio and N contents of the material for composting did not influence the rate of organic nitrogen accumulation in the compost,nor the change tendency of the organic N components.After composting, the proportions of the amino acid-N and ammonia-N of the total hydrolyzable N were increased with the material rich in protein and those of the acid-insoluble N and the unidentifiable N were increased with the material rich in lignin and cellulose.The 15N added to the compost mainly constructed the amino acid-N of the organic N components.The addition of the(¹⁵NH₄)₂SO₄ during the temperaturedecreasing stage could increase the proportion of the amino acid-N.Labelling compost directly using ¹⁵N had decreased its loss and increased its transformation rate compared with labelling the material for making compost