Aim of the study: The aim of the present study was to synthesize and characterize a new calcium phosphate based root repair material (SCPC) and it's comparison with Bioaggregate (BA) and mineral trioxide aggregate(MTA). Materials and methods: The cement formulation consisted of two parts; a powder mix containing dry calcium phosphate particles and a wetting medium prepared with distilled water. SCPC, BA and MTA were assessed for the following; Surface topography by scanning electron microscopy, elemental analysis by energy dispersive X-ray spectroscopy, pH by digital pH meter and calcium ion by atomic absorption spectroscopy. Evaluation of the intra-osseous biocompatibility of the three cements was carried out in six mongrel dogs where they were placed in surgical created defects in the mandible in such a way that every defect received one of the three tested materials leaving the fourth defect empty serving as a negative control group. Animals were sacrificed; specimens were prepared for histopathological evaluation, scoring of the inflamed tissue, area percent of granulation tissue, mineralized bone and fibrous tissue were calculated by Image analysis software. Usage test of BioAggregate as compared to MTA in 14 selected clinical cases indicated for periradicular surgery. Imaging was performed by using a Trophy X-Ray machine; the images were digitized by the Digora system. Retrocavities were prepared followed by the placement of root end filling material either BA or MTA. Clinical and radiographic postoperative evaluation was done after 3 and 6 months to assess healing. Results: As for elemental spot and area analysis of SCPC, BA and MTA showed that the principal chemical component in them was oxygen, calcium and silicon. Examination of the micrographs of the 3 samples revealed that the presence of coarse crystalline particles in a general ground mass of finer amorphous material (semi crystalline) of calcium silicate hydrate. The three groups showed a decrease in pH and calcium ion release along the 3 hydration periods with MTA showing the statistically significant highest percent decrease in pH. Regarding biocompatibility study, all groups showed decrease in inflammatory scores along the observation periods. Kruskal-Wallis and Mann-Whitney U tests showed that there was no statistically significant difference between SCPC and negative control groups. MTA showed the statistically highest percent increase in mineralized bone followed by SCPC. Results of the usage test showed the following: Two patients dropped out of the study. Using unpaired t-test there was no statistical significant difference found between bone densities at 3 and 6 months between BA and MTA groups. Conclusions: it was concluded from the previous study that SCPC showed high levels of calcium ion release which decreased with progressive periods of hydration, the pH of SCPC decreased along periods of hydration but still remained on the alkaline side. At the level of the present study it was found that SCPC was biologically compatible. Key words: calcium phosphate cements, Bioaggregate, biocompatibility, root end filling.