A group of solid adsorbents in the form of powder, granules or pellets having improved adsorptive capacity and selectivity for ethylene and/or propylene is disclosed. These adsorbents comprise (a) a silver compound and (b) a bentonite clay support bulk of which comprises SiO2 and Al2O3 and the rest being oxides of Fe, Ca, Mg, Na and K and having sufficiently high surface area on which the silver compound is dispersed or impregnated. The support may be pretreated by polymer solutions to impart sufficient mechanical strength as measured by attrition loss. Mechanical strength may also be improved by pre-heating the support. These adsorbents are highly stable and are capable of reversibly adsorbing substantial quantity of ethylene and/or propylene at room temperature. The rates of adsorption of ethylene and/or propylene are also very high in these adsorbents, which is believed to be due to the synergistic interaction between the components of the novel composition of the present invention.