Mulching is considered as a simplest utilization of water hyacinth. In this study, a field experiment using the litterbag method was conducted on the decomposition of the water hyacinth mulch under vegetable plot conditions. Mulch mass losses and changes in nutrient and C/N ratio were measured over 100 days to determine the effects of mulch characteristics on decomposition and nutrient concentration in the remaining mulches. The remaining mass after 100 days decomposed on the vegetable plot was 45.4%, 9.4% and 0.0% to the initial mass of the root, stem and leaf, respectively. Water hyacinth leaf recorded the highest decomposition rate 0.1538 day-1 7 times greater than stem, with stem 0.0217 day-1 but significantly greater than root 0.0072 day-1. The time taken for 95% mass loss varied with mulches. Root took 403 days, stem took 130 days and leaf took 36 days, respectively. The remaining N of leaf mulch decreased with decomposition time. On the other hand, the remaining N of root and stem showed three phases: decreased (reaching 42.0% and 26.2%), increased (reaching 44.8% and 26.5%) and decreased again (reaching 32.5% and 8.0% of the initial N content of the root and stem). The remaining P of stem and leaf declined continuously from the beginning to the end of the study. The dynamic of the P of root can be divided into two phases. In the end of the experiment the C/N ratio was 25.5, 24.7 and 19.4 of the root, stem and leaf, respectively. The results demonstrated that the leaf decay first and the root can last for more than 1 year during the water hyacinth mulch decomposition, this may be good for the soil nutrient cycling and moisture conserving under vegetable plot.