P4 generated from red phosphorus via the gas phase was trapped into an interactive pore of a porous coordination network, showing weak interactions which stabilize the reactive P4 in a pore. The network is reusable as a safe container of P4. Furthermore, we found a size dependence of the P4 trapping amount: for 100-50 μm crystal, 27% occupancy of P4; and for <20 μm crystal, ca. 93% occupancy of P4.