The effects of soil water regime and soil reaction on nitrogen distribution and fractional composition of newly-formed humus (decayed products) and the structural characteristics of the newly-formed humic acids (HAs) were studied in an incubation experiment, with the following results obtained:1. The humus newly formed under submerged conditions was higher in the relative content of α-amino acid-N and the humic acid/ fulvic acid (HA/ FA) ratio than that under upland conditions. The HAs extracted from the former were also higher in C / O ratio, aromaticity and the contents of methoxyl groups and lignin-like components, but lower in the content of carboxyl groups than the HAs from the latter.2. Under upland conditions, the C / organic N ratio and the relative content of mobile HA of newly-formed humus were lower, but the HA / FA ratio was higher in the CaCO3-amended treatment than in non-amended treatment. The presence of CaCO3 also resulted in a decrease of C / N ratio of HA and a slight increase of its The effects of soil water regime and soil reaction on nitrogen distribution and fractional composition of newly-formed humus (decayed products) and the structural characteristics of the newly-formed humic acids (HAs) were studied in an incubation experiment, with the following results : 1. The humus newly formed under submerged conditions was higher in the relative content of α-amino acid-N and the humic acid / fulvic acid (HA / FA) ratio than that under upland conditions. The HAs extracted from the former were also higher in C / O ratio, around and the contents of methoxyl groups and lignin-like components, but lower in the content of carboxyl groups than the HAs from the latter. Under upland conditions, the C / organic N ratio and the relative content of mobile HA of newly-formed humus were lower, but the HA / FA ratio was higher in the CaCO3-amended treatment than in non-amended treatment. The presence of CaCO3 also resulted in a decrease of C / N ratio of HA and a slig ht increase of its