A new method for preparing high bending strength porous silicon nitride ceramics with controlled porosity has been developed by using a pressureless sintering technique with zirconium phosphate (ZrP 2 O 7 ) as a binder phase. The sintering behavior in these porous ceramics is investigated in this study by using XRD, SEM, and HRTEM analysis. The results show that the sintering process can be divided into two stages: one is at temperatures below 250°C, during which ZrO 2 can react completely with H 3 PO 4 to form ZrP 2 O 7 , and a ZrP 2 O 7 bonded Si 3 N 4 porous structure is formed; the other is at temperatures above 250°C, at which solid state sintering of the ZrP 2 O 7 dominates and a continuous open porosity network is obtained. The effect of the ZrP 2 O 7 binder content on sintering behavior, porosity and mechanical properties is also investigated.