Hydroxyapatite (HA) is a crystalline molecule composed of phosphorus and calcium with the molecular formula Ca10(PO4)6(OH)2. HA occupies 70% of the mineral fraction present in human bones and this material is also present in the structure of human teeth, especially in dentin and enamel. HA is mostly synthesized from untapped natural materials. In this research, HA synthesis has been carried out from the shells of serai snails and mangrove crabs at TanjungJabung Barat Jambi Beach using the dry method with variations in sintering temperature. HA which is synthesized from snail shell produces HA phase, while what is synthesized from crab shell produces β-tricalcium phosphate (β-TCP) phase. The diffraction pattern shows that the higher the sintering temperature, the higher the intensity and the narrower the peak, this has an effect on the degree of crystallinity and the size of the HA crystals. The FTIR spectrum showed the presence of PO43- and OH groups from HA. Analysis using the Particle Size Analyzer (PSA) showed that the higher the sintering temperature the larger the particle size.