Laboratory batch experiments were conducted, using suspended solids and sediments taken. from a tidal section of the Rokkaku river, to study the effect of salinity on nitrification and to estimate kinetic parameters of it. Experimental results indicated much more inhibitation of ;$NO_2$-N oxidation by chlorides than that of $NH_4$-N oxidtion. Nitrifying bactema in sediments were less sensitive to chlorides than those in SS. The change of nitrogen concentration with time was clearly explained with the Monod growth model and the kinetic parameters were obtained by the curve fitting method.