The structure and modules for a model of soil organic matter (SOM) dynamics simulating the role of soil fauna in humification are described. The contributions of micro- and meso-fauna to SOM formation are described using a food web module. The contributions of anecic earthworms to SOM formation are described using a module in which processes occurring in fresh casts play a key role in SOM stabilisation. Model testing showed accumulation of faunal by-products in the well-decomposed SOM of the organic soil horizons and the stable SOM of the mineral soil.