Apatitic layered octacalcium phosphate (Ca₈(HPO₄)₂ (PO₄)₄⋅5H₂O; OCP) was intercalated with β-dihydromuconate ions (-OOC(R)COO-, R; CH₂-CH=CH-CH₂). The basal spacing of the OCP structure was expanded to 23.7Å by the intercalation (OCP: 18.7Å). The spacing was contracted by heating (dehydration), and reverted by exposure to H₂O vapor (rehydration). Such zeolite-like behavior toward H₂O was observed below 350°C. A remarkable contraction in the basal spacing by dehydration suggested the bending of zig-zag R chains supporting the layer structure. Improvement of the thermal stability of the OCP layer structure was judged from increases in starting temperatures for the following processes: 2HPO₄^2-→P₂O₇^4-, formation of apatitic OH^-, disappearance of OCP phase and appearance of apatitic phase. No significant differences were observed in thermal behavior between the intercalates of the doubly unsaturated R and saturated R, i.e., CH₂-CH₂-CH₂-CH₂, were a little. The intercalation decreased the catalytic activity for the dehydration of 2-propanol.