Insitusurvey of river salinity using a portable neutron‐gamma probe was conducted at northern Taiwan. The probe, consisting of a 40 &mgr;g282Cf neutron source and a HPGe detector, was mounted on board a fishing boat to survey the salinity at river delta. The variations of water salinity along the river were mapped according to the tidal cycle. Detecting range, radiation doses, characteristics of theinsituprompt gamma spectrum, and its potential application as a salinometer are discussed.