Anthropogenic radioactivity in the northern Adriatic Sea was assessed by analysing 137Cs in seawater and sediment. Radiological observation was done by analysing the sediment surface layer and seawater at different depths (0, 15 and 30 m) at the Po River delta (station 108) in the period from January 2014 to August 2015. 137Cs activity concentrations in the sediment were in the range between 6.88 to 8.75 Bq kg-1 in the observed period while 137Cs concentration measured in seawater were ranged from 0.862 to 2.95 Bq m-3. Higher average 137Cs activity concentrations in the sediment of the Po River delta in compared with the sediment of the Rovinj coastal area indicate that the discharge from the Po River could be an important supplier of 137C to the northern Adriatic. It was also found that differences in 137Cs concentration were not significant between investigated layers of seawater. The decreased trend of 137Cs concentration activity with the depth at station 108 is not expressed. In the area of the Po River delta, concentrations of 137Cs in seawater are now lower than pre-Chernobyl values, generally taking into consideration the natural fluctuation due to the physico-chemical and hydrographic parameters of the investigated area.