Cylindrical samples of sediments have been obtained from four sea areas adjacent to the Mirs Bay to the east of Hong Kong. An n-type HPGe low background γ-ray spectrometry system has been employed to measure the Pb-210 and Cs-137 concentrations in the samples simultaneously. The distribution of the specific activities with depth were also acquired. The results show that the sedimentation rate decreases when the sampling sites are further away from the Mirs Bay into the South China Sea. The Cs-137 method yields results which are subjected to external disturbance to a greater extent, and is thus less reliable than the Pb-210 method.