Abstract A study on hydrogen uptake performance of Gamma (γ)-ray irradiated multi-walled carbon nanotubes (MWCNTs) was conducted. Initially, the MWCNTs was irradiated by γ-rays emitted from 27Co60 source with different doses of 25, 50, 100, 150, and 200 kGy in air at ambient conditions. Irradiation at lower doses of 25 and 50 kGy improves the graphitic order of MWCNTs, but higher doses of 100 and 150 kGy introduces structural imperfection and at very high dose of 200 kGy, the structure becomes distorted. Thermogravimetry (TGA), X-ray diffraction (XRD), Raman spectroscopy, I-V measurements, and Transmission electron microscopy (TEM) confirm the changes in MWCNTs caused by irradiation. Further, the γ-irradiated MWCNTs was hydrogenated and the MWCNTs irradiated at 150 kGy exhibits a considerable hydrogen storage capacity of 1.2 wt.% at 100 °C and ambient pressure, while the MWCNTs irradiated at lower doses does not show any trace of hydrogenation. Raman and elemental analyses provide the evidence for hydrogenation.