We found that polycyclic aromatic hydrocarbons (PAHs) such as pyrene and phenanthrene can be encapsulated in a syndiotactic poly(methyl methacrylate) (st-PMMA) helical cavity, leading to the formation of a crystalline inclusion complex. The inclusion complex of st-PMMA and pyrene (st-PMMA/pyrene) was prepared from the st-PMMA gel formed in a toluene solution of pyrene by drying under vacuum at room temperature for 12 h and at 160 degrees C for 1 h. The st-PMMA/pyrene inclusion complex containing 19 wt 96 pyrene showed a characteristic reflection pattern in its X-ray diffractogram and a melting point of 184.4 degrees C in differential scanning calorimetry experiments. Molecular modeling of the inclusion complex based on the pyrene content indicated that the encapsulated pyrene molecules are closely aligned in the st-PMMA helix. The st-PMMA/pyrene inclusion complex film containing 10 wt % pyrene showed a fluorescence emission because of the formation of a pyrene excimer in the complex, supporting the inference of one-dimensional alignment of the guest molecules in the st-PMMA helical cavity.