Water-compatible molecularly imprinted polymers (MIPs) for caffeine were synthesized in aqueous medium with a new functional monomer, 1-(a-methyl acrylate)-3-methylimidazolium bromide (1-MA-3MI-Br), which had p-p and hydrogen-bonding interactions. Caffeine-imprinted polymers were prepared in suspension polymerization with 1-MA-3MI-Br and methacrylic acid (MAA), which only had hydrogen bonding, as a functional monomer. For the specific binding characteristics of the new functional monomer 1-MA-3MI-Br, the adsorption capacity and relative separation factor (b) of MIPs for caffeine were significantly enhanced. The maximum adsorption capacities of 1-MA-3MI-Br-MIP and MAA-MIP imprinted microspheres for caffeine were 53.80 and 28.90 lmol/g, respectively. Moreover, the relative separation factors were measured by comparison of the separation characteristics under competitive adsorption conditions. The results showed that the b of MAA-MIP for caffeine relative to theophylline was only 1.65; this showed a very poor recognition selectivity for caffeine, but b of 1-MA-3MI-Br-MIP for caffeine with respect to theophylline was remarkably enhanced to 3.19; this showed an excellent recognition selectivity and binding affinity toward caffeine molecules in an aqueous environment.