Objectives: sealing ability and apatite forming ability (bioactivity) of a new endodontic sealer based on calcium-fluoro-silicate hydraulic cement were tested. Methods: extracted single-rooted teeth were instrumented with ProTaper rotary instruments, irrigated with NaOCl, EDTA, and filled with single-cone gutta-percha (Hygienic,USA) in association with TECHBiosealer Endo (Isasan,Italy) (N=10) or CRCS (Hygienic,USA) (N=10). The apical leakage was measured after 24 hours, 1,4 weeks and 3 months of aging in simulated body fluid (Hanks' Balanced Salt Solution, HBSS) at 37°C by a digital fluid flow-meter (University of Bologna, Italy). The bioactivity i.e. apatite formation ability was assessed by ESEM/EDX, micro-Raman and FTIR analyses on materials as-prepared or aged for 6,24 hours and 1,4 weeks in HBSS. Results: TECHBiosealer group showed statistically lower apical microleakage than CRCS group. Statistical differences in fluid flow (p<0.05) among the sealers were found at all analysis time-endpoints. The seal of TECHBiosealer endo was stable over time, showing the following apical leakage (μL/min): 0.043 ± 0.038 at 24 hours, 0.025 ± 0.020 at 1 week, 0.040 ± 0.015 at 4 weeks and 0.079 ± 0.035 at 3 months. Differently fluid flow of CRCS increase over time (μL/min): 0.106 ± 0.117 at 24 hours, 0.139 ± 0.176 at 1 week, 0.128 ± 0.105 at 4 weeks and 0.232 ± 0.227 at 3 months. ESEM of fresh TECHBiosealer showed the formation of a dense gel and many crystals on the surface after 6 hours in HBSS. EDX revealed high amounts of calcium and silicon on fresh, 6 and 24 hours-aged samples, while Ca and P were found on 1 week and on 1 month-aged samples. Diffuse deposits of apatite spherulites were detected on 1 and 4 weeks-aged TECHBiosealer samples. Micro-Raman and FTIR analyses showed C-S-H and calcium-hydroxide bands after 6 hours, whereas apatite bands were observed after 24 hours in HBSS. No bioactivity was demonstrated by CRCS. Conclusions: TECHBiosealer Endo has the capacity to form apatite and possess an apical sealing ability better than CRCS. Early calcium-hydroxide and C-S-H gel formation promote the nucleation of apatite deposits. The formation of apatite improve the apical sealing.