The sodium alginate(SA)/poly(N-isopropylacrylamide) (PNIPAM) semi-interpenetrating (semi-IPN) hydrogel was prepared by incorporating SA into cross-linked PNIPAM to form a semi-IPN polymeric network．The properties of the semi-IPN hydrogel were characterized by DSC and SEM．The influences of the amount of SA in the semi-IPN hydrogel

pH and temperature on the swelling rates of these hydmgels have been thoroughly investigated．It is showed that at a temperature below the lower criffical solution temperature (LCST) and pH=7.4 the swelling rate increases with increasing SA content in the semi-IPN hydrogel and relies on the relaxation rate of macromolecular chains in the hydrogel network．In addition

the effect of pH value on the swelling rate depends on temperature

while the effect of temperature on the swelling rate is also associated with pH value.