Microcellular foam injection molding process with core-back expansion operation has a potential of producing high expansion foams with fine cellular structure. In our previous study, using a 35 tonnage Mucell® foam injection machine with core back operation, a high expansion open porous polypropylene (PP) microcellular foam was successfully prepared. The crystal nucleating agent was used as a nucleating and gelation agent so as to control the cell opening. At highest expansion ratio with 0.5 wt% of the crystal nucleating agent, the open cell content (OCC) could reach higher than 90 %. Open porous polymeric foams were attractive, however, it is more useful if the degree of the OCC could be controlled. In this study, a low tacticity polypropylene with low modulus (LMPP, 700G, Idemitsu Kosan) was used as a OCC controlling agent. It was blended with high tacticity isotactic polypropylene (i-PP, F133A, Idemitsu Kosan) and used to control the OCC. The addition of LMPP to high tacticity i-PPs prevented the cell opening or fibrillation, and it could keep the closed cell structure even when the expansion ratio became fivefold. For example, high expansion microcellular foams with closed cell structure was prepared from i-PP/LMPP blend with the 80/20 weight ratio by the foam injection molding with coreback operation. When the i-PP alone was foamed, the OCC reached 20 % at the two-fold expansion ratio and increased to 50% at the five-hold expansion. For i-PP(F133A) with 0.5 wt % of the crystal nucleating agent, the OCC was 50 % at two-hold expansion and it became 90% at the five-hold. When the LMPP was added to the i-PP, the OCC was kept to be less than 20 % for any expansion ratios in the range 2 to 5. This clearly shows that the spin-ability and stretch-ability of the LMPP affects cell morphology and reduces the OCC. In the presentation, the other experimental results obtained from the i-PP/LMPP at the different blend ratios will be introduced to confirm the OCC controllability of LMPP at the high expansion foams.