Phase transformations in solutions of syndiotactic polystyrene in cis-decalin has been investigated by differential scanning calorimetry, wide and small angle X-ray scattering, and Fourier transformed infrared spectroscopy. The in-situ performed experiments enabled identification of the different modifications without solvent removal. Quenching a solution leads to formation of the helical δ-phase. On heating, this phase transforms into the planar zigzag β-phase. The transformation of the helical phase (δ) into the planar zigzag (β) during heating proceeds via a melting-recrystallization process.