In this study, measurements of the solubilities of pure carbon dioxide, pure helium, and a feed mixture of 4096 CO2-He balance were carried out in the ionic liquid, 1-butyl-3-methyl-imidazoliumdicyanamide ([bmim][DCA]). Measurements were also made in its solution containing 20 wt % and 30 wt % poly(amidoamine) (PAMAM) dendrimer Gen 0 with and without moisture. A pressure-decay dual-transducer apparatus was employed at temperatures of 323, 353, 363, and 373 K and at pressures up to 1.38 MPa (similar to 200 psig). Henry's law constants of pure CO2 and pure helium were determined at different temperatures for the ionic liquid. Pseudo-Henry's law constants for each of CO2 and helium in a 40%-60% feed gas mixture were also determined. Solubility selectivities of carbon dioxide to helium for all liquid absorbents were also calculated at each temperature. Carbon dioxide was absorbed much more in these studied liquids, compared to helium. In addition, carbon dioxide absorption increased considerably when the amine was added to the ionic liquid and then increased several-fold when moisture was present in the amine ionic liquid solution, compared to the CO2 absorption by the ionic liquid.