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We present a Raman spectroscopy study of the vibrational properties of free-base meso-tetra(4-pyridyl) porphyrin polycrystals under various temperature and hydrostatic pressure conditions. The combination of experimental results and Density Functional Theory (DFT) calculations allows us to assign most of the observed Raman bands. The modifications in the Raman spectra when excited with <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mn>488</mn><mo> </mo><mi mathvariant="normal">n</mi><mi mathvariant="normal">m</mi></mrow></semantics></math></inline-formula> and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mn>532</mn><mo> </mo><mi mathvariant="normal">n</mi><mi mathvariant="normal">m</mi></mrow></semantics></math></inline-formula> laser lights indicate that a resonance effect in the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mrow><mi mathvariant="normal">Q</mi></mrow><mrow><mi mathvariant="normal">y</mi></mrow></msub></mrow></semantics></math></inline-formula> band is taking place. The pressure-dependent results show that the resonance conditions change with increasing pressure, probably due to the shift of the electronic transitions. The temperature-dependent results show that the relative intensities of the Raman modes change at low temperatures, while no frequency shifts are observed. The experimental and theoretical analysis presented here suggest that these molecules are well represented by the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mrow><mi mathvariant="normal">C</mi></mrow><mrow><mn>2</mn><mi mathvariant="normal">v</mi></mrow></msub></mrow></semantics></math></inline-formula> point symmetry group.