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Properties such as gamma shielding, cure characteristics, and mechanical properties of natural rubber (NR) system with addition of oxides such as: iron (II, III) oxide (Fe3O4), tungsten (III) oxide (W2O3), or bismuth (III) oxide (Bi2O3) were studied for potential replacement of flexible lead (Pb), and introduced as gamma-shielding materials, to minimize risks caused by Pb. The results showed that increase in the content of oxides such as Fe3O4, W2O3, or Bi2O3from 0 to 100, 300, and 500 parts/100 parts of rubber by weight (phr) increased the gamma attenuation coefficients, tensile modulus at 100% elongation, and hardness (Shore A), though they reduced the tensile strength and elongation-at-break. The composites also underwent thermal aging tests at 70 °C for 96 h. The results indicated slight reduction in the overall tensile properties. Specifically, for NR composites with 300 or 500 phr of Bi2O3, the mass attenuation coefficients (μm) of these composites were the highest among other composites and even higher than lead sheets that were measured using the same set-up. The outcome of the results imply great possibilities of replacing hazardous lead-containing gamma-shielding materials with the investigated composites, while still providing safe and efficient gamma-shielding properties for the users.