It was shown experimentally that the rate of aliphatic nitrocompounds decomposition in supercritical water (SCW) depends on pressure/density at constant temperature. The SCW density dependence of the apparent rate constant of decomposition for each of three compounds under consideration (nitromethane, nitroethane and 1-nitropropane) was found to correlate with the density dependence of the H3O+ concentration in dissociated SCW The rate constant of RNO2 decomposition in SCW decreased with increasing the length of hydrocarbon radical R. (C) 2004 Elsevier B.V. All rights reserved.