Raman spectroscopy has been used for the first time for the characterization of perfectly 1:1 alternating a-olefin:carbon monoxide aliphatic polyketones produced by the polymerization of ethene with carbon monoxide (ECO polymers) and mixtures of ethene and propene with carbon monoxide (EPCO polymers). A procedure to determine the methyl branch content arising from propene incorporation in EPCO polymers was established. This is based on the good correlation found between the intensity of a Raman band assigned to -CH3 bending and the propene incorporation determined by H-1 NMR spectroscopy. A measure of the relative degree of crystallinity was made from the CO stretching band, and this was correlated with the heat of fusion determined by differential scanning calorimetry. Band shapes in the range assigned to -CH2- bending were attributed to factor group splitting effects (correlation splitting) and were interpreted to infer the presence of the two crystal forms (alpha and beta) which have previously been identified by X-ray diffraction for aliphatic polyketones.