Abstract: Novel microporous particles of polybenzimidazole (PBI) resin, characterized by a reduced bulk density, a surface area of at least 10 m.sup.2 /g, a porosity of at least about 10%, and an average pore diameter of from about 50 to 500 Angstroms are provided by emulsification-precipitation or atomizing-non-solvent quenching techniques. The disclosed microporus PBI particles are particularly suitable for use as substrates in chromatographic processes such as ion-exchange, separations, purifications, etc., as well as catalysts or chemical reagents in polymer supported reactions. Microporous PBI particles of varying acidity/basicity and/or anionic/cationic exchange characteristics, and/or containing various functional groups for use in chemical conversions, may be obtained by treatment of the PBI resin with various organic and inorganic acids, either during particle formation or subsequent thereto.