It is necessary to understand the heterogeneity in necromass and carbon (C) and nitrogen (N) contents within a dead bamboo culm before estimating these parameters in dead culms. This study determines differences in necromass and C and N contents between node and internode material of decomposing bamboo culms. We collected dead culms of Phyllostachys bambusoides and P. pubescens from 11 bamboo stands in central and south-western Japan, and determined the necromass per culm cylindrical volume (culm volume density), the C and N stocks per culm cylindrical volume (C and N densities), and the C and N concentrations of node and internode material. In both species the culm volume density was greater in node than internode, which led to a greater C density in node than internode, whereas the C concentration scarcely differed between the two. The N density was greater in node than internode material in both species, due to the difference in culm volume density, while the N concentration was also greater in node than internode. These differences remained unchanged with the degree of decomposition, because the dynamics of necromass and C and N were similar for node and internode materials. The decomposition process in node and internode resembles that in dead wood although variation in N dynamics is observed for P. bambusoides. When the greater culm volume density and C and N densities in node than internode were not taken into account, the necromass and C and N stocks in a dead bamboo culm decreased by 4.46-4.50, 4.51-4.59 and 9.47-10.83% respectively. We must sample numerous dead culms to mitigate node and internode differences. However, it might be better to take into account these differences when the number of dead culm samples is limited.