In this study, polyurethane foams (PUF) were prepared using alginic acid, glycerin, and poly(ethylene glycol) (PEG) as polyols, 1,6-hexamethylene diisocyanate (HDI) as a diisocyanate, and water as a foaming agent by one-shot process. Their structural, mechanical, and water-absorbing properties were investigated. The amount of alginic acid was varied up to 30 wt%. Fourier transform infrared (FT-IR) analysis showed that urethane linkage was formed by the reactions between -NCO groups of diisocyanate and -OH groups of all polyols used. Also urea linkage was formed by the reactions between -NCO groups of HDI and water or $-COO^-$ groups of alginic acid. The reaction times for cream forming increased with increasing alginic acid but foam structures were not formed when alginic acid content in polyols was above 30 wt%. The optical micrographs showed that the average cell size of PUF slightly increased with increasing alginic acid. However, the density of PUF decreased with alginic acid content. The compressive modulus of PUF decreased with increasing alginic acid content. In the mean time, the water absorbency of PUF increased with increasing alginic acid content.