We have synthesized water-soluble poly(arylene ethynylene)s having maleimide groups capable of reacting with thiol-containing biomolecules. The number-average molecular weights of the polymers range from 11,000 to 14,000. The polymerization was carried out by palladium-catalyzed Sonogashira-Hagihara cross-coupling reaction with good yield. The polymers showed blue emission colors in their methanol solutions, while green color was observed in aqueous solutions with decreased emission intensity.