Monodisperse polyacrolein (PA) microspheres were prepared by means of emulsifier-free emulsion polymerization of acrolein in aqueous medium using sodium hydroxide as catalyst. The diameter of PA microspheres prepared was in the range from 1.45 to 2.21um

the capacity of reactive aldehyde groups was in the range from 2.591 to 5.199 mmol per gram PA microspheres. The optimum polymerization condition was: acrolein

7-10%(w/v); pH

8.5-11.2; temp.

16℃; time

3.5hr. The diameter of PA microspheres changes with concentration of catalyst and acrolien. The capacity of reactive aldehyde groups of PA microspheres chan-ges with the reaction conditions

e.g.

the capacity of reactive aldehyde groups of PA micros-pheres increases with the decrease of the catalyst concentration when pH>10. The results of PA microspheres reacting with amino acids and bovine serum albumin at physiological pH ran-ge showed that the PA microspheres have a higher biding capacity.