Composting of source-separated organic household wastes is becoming a more common practice in several countries. Carbon decomposition dynamics during composting are important for an overall understanding of the process. We investigated over 590 days losses of organic C and decomposition of C constituents in artificial organic household waste mixed with six different litter amendments; straw, leaves, hardwood, softwood, paper and sphagnum peat. Litter addition was necessary to achieve an aerobic process. Samples were analysed for dry matter, ash, organic C, volatile fatty acids, and lignin, cellulose and hemicellulose fractions. Calculated by first-order kinetics, residual amounts of dry matter were 22-63% and of organic C 11-61%, and both amounts were highest in the peat mixture and lowest in the control without litter addition. Rate constants for dry matter and organic C decomposition were highest in the leaf mixture and lowest in the control. The initial lignin content in the mixtures was highly correlated (R-2 = 0.91) with the residual amount of organic C. A lag phase, of varying length, in lignin decomposition was present in some but not all cases. Cellulose decomposition was slower in leaf, hardwood and softwood mixtures than in paper and straw mixtures. The results showed that the characteristics of litter amendments greatly influence the composting process.