Variations in hexeneuronic acid content in hardwood alkaline pulps were investigated to evaluate their contribution to kappa number. Out of diverse chemical pulps the highest hexeneuronic acid content were measured in yellow poplar kraft pulping, which was assumed to enhance ca. 7.0 of kappa number determined by acid permanganate consumption. In yellow poplar soda-anthraquinone pulping, hexeneuornic acid was contributed to increment of 5.0-6.0 kappa number. In eucalyptus alkaline pulping, hexeneuronic acid content was not significantly different from soda-anthraquinone pulping. Increment of Kappa number by hexeneuronic acid was 4.5-5.6 depending on pulping method and pulping time at target temperature.