Density functional theory has been employed to optimize the structure of endohedral doped C 20 fullerene. We have also investigated electronic properties. We have found that C 20 cage can accommodate up to 8 hydrogen atoms. Some hydrogen atoms get chemisorbed on the inner surface of C 20 cage and form C–H bond. Structural deformation is found to increase with increase in H-atoms. From the analysis of electronic properties, we observe that due to endohedral doping of hydrogen atoms inside C 20 , H-atoms acquire net negative charge by accepting electrons and fullerene molecules acquire positive charge by donating electrons to H-atoms. For endohedral complexes where H 3 triangular molecule formation takes place, the nature of net charge transfer changes, i.e. fractional electronic charge is transferred from H-atoms to fullerene. C 20 doped with odd number of H-atoms should be more reactive compared to the even number case. Most of the present results are similar to those of endohedral C 60 .