Objective: To prepare and characterize composite scaffolds of a hydroxyapatite (HA) and an alginate having high viscosity. Materials and Methods: HA powder was synthesized using wet chemical precipitation, the alginate powder was extracted from the Sargassum duplicatum seaweed, and the HA/alginate composite scaffolds were prepared by freeze-drying. X-ray diffraction and Fourier transform infrared techniques were utilized to characterize the HA and alginate, and electron microscopy was used to evaluate the HA and the HA/alginate composite scaffolds. The HA/alginate composite scaffold obtained from the commercially available HA and alginate powders were employed as a comparison. Results: Synthesized HAs were identified as the HA phase, which contained absorbed water, phosphate, and carbonate groups. The extracted alginate contained the carboxyl, cyclic ether and hydroxyl groups. The scaffolds prepared from the HA and alginate mixture were three-dimensional and containing interconnected pores with a diameter ranging from 150 to 300 µm and pore walls of a composite construction. Conclusion: A three-dimensional scaffold was produced using a freeze-drying method from a composite of HA and the high viscosity alginate solution. The scaffold was highly porous and showed interconnected pores, with a diameter ranging from 150 to 300 µm.