We have been successful in growing well-defined polygon crystals of fullerene and pentacene in liquid and vapor phases, respectively. These crystals were grown directly or laminated on substrates, allowing us to carry out their detailed structural characterization. We estimated the crystal structure of fullerene crystals by comparing the results of microscope and X-ray diffraction (XRD) observations with the crystal structure of a solvate. We carried out spectroscopic and XRD measurements on the pentacene crystals. Combining density functional theory calculations with the polarizing microscope observation, we related the principal axes of refractive index to the crystal geometry of pentacene.