The considerable number of important physical properties, including optical, electronic, and magnetic properties, of Prussian blue (PB) analogues have attracted fundamental and industrial interest. Nevertheless, the gas sorption properties of PB coordination compounds were only investigated very recently. In this work, we report the synthesis and gas sorption properties of PB nanocomposites with different size and shape obtained by using poly(vinylpyrrolidone) (PVP), chitosan, and dioctyl sodium sulfosuccinate (AOT) as stabilizers and structure directing agents. All three porous nanocrystals show high and selective CO2 adsorption over CH4 or N-2. No distinct relationship was found between the size (or shape) of the nanosorbents and their gas uptake capacities. To our knowledge, this is the first report on the use of PB nanocomposites for CO2 capture applications.