Caspase-12, mainly detected in endoplasmic reticulum (ER), has been suggested to play a role in ER-mediated apoptosis and inflammatory caspase activation pathway. Removal of the prodomain by caspase-3/-7 at Asp94 or m-calpain at Lys158 was reported to be a part of caspase-12-involved (in) apoptosis. To provide biochemical background for the processes, we purified and characterized three forms of caspase-12; ${Delta}pro1$(G95-D419), rev-${Delta}pro1$[(T319-N419)-(G95-D318), a reverse form of ${Delta}pro1$] and rev-${Delta}pro2$[(T319-N419)-(T159-D318)]. Activity of ${Delta}pro1$, comparable (in compare) to those of the other two, decreased significantly under the physiological salt concentration and pH or by mutations at both Asp318 and Asp320. These indicated (indicate) that activation of caspase-12 may need pH drop and ion efflux observed during apoptotic process, and auto-proteolytic cleavage at the sites. Furthermore, constitutively active forms of caspase-12 could induce cell death, but no cleavage of caspase-3, DFF45 and Bid was observed, implying involvement of caspase-12 in a distinct way rather than in the well-known pathway.