In this study eleven groundwater sources includes wells and springs in Siwa oasis, Egypt were subjected to radioactivity measurement and assessment during the period from June (2014) to July (2014). Siwa oasis located 65 km east of the Libyan frontier and 300 km south of the Mediterranean coast and around 800 km west Cairo. The collected water samples were acidified in the field then transferred to radiation measurement laboratory at Institute of Graduate Studies and Research, Alexandria University. The samples were prepared for gamma rays spectroscopic analysis by high purity germanium gamma rays spectrometer. Radionuclides 238 U, 226 Ra, 228 Ra, 40 K measurements were performed according to method of IAEA. The obtained radioactivity concentrations displayed ranges (2.3-11.28)Bq/L,(0.08-7.47) Bq/L, (0.472-4.1) Bq/L, and (0.0245-5.33) Bq/L for 238 U, 226 Ra, 228 Ra and 40 K, respectively. Radiological effects due to internal radiation exposure via drinking water from studied wells indicated annual effective doses ranged from 0.71mSv/year to 3.79mSv/year. Lifetime cancer risk and genetic risk due to these radiation levels were calculated to be ranged from2749× 10-6 to14592× 10-6 and from 499× 10-6 to 2653 × 10-6 for cancer risk and genetic risk, respectively.