Porous scaffold containing biodegradable Ca-crosslinked alginate(ALG) and nano-hydroxyapatite(n-HA) is synthesized by the freeze-extraction and freeze-gelation methods. The prepared scaffolds were tested by scanning electron microscopy (SEM), transmission electron microscopy (TEM), infrared absorption spectra (IR), raman spectra, X-ray diffraction (XRD) and burning test. Chemical binding between inorganic n-HA and Ca-crosslinked alginate was investigated. It indicated that n-HA was interacted with Ca-crosslinked alginate. The results of SEM showed that the scaffolds exhibited open-cellular pore structures. The content of n-HA affected the porosity and pore size of the composite. The composite can be a promising scaffold material for tissue engineering.