There are mainly two varieties of cinnamon available on the European market – Ceylon and Cassia cinnamon. Cassia cinnamon differs from Ceylon cinnamon in the taste, smell, appearance and, most of all, in the content of coumarin. Cassia cinnamon contains up to 10.6 % of this compound, whereas Ceylon cinnamon contains only trace amounts thereof. The objective of the research study was to assess the quality of cinnamon marketed in Poland using HPLC method. There were analysed twenty-six commercial samples in the form of powder (n = 19), sticks (n = 6) and bark (n = 1) in order to determine the contents of coumarin and cinnamaldehyde therein. Among them 73 % had no information of their botanical origin shown on their labels (they were marked with the “unknown origin” indication). The samples labelled as Cinnamomum verum (n = 6) or Cinnamomum cassia (n = 1) were used as reference samples. The samples of unknown origin were characterised by the highest content of coumarin (2.3 ÷ 7.7 mg/g) and the C. verum and C. cassia samples by  the lowest content thereof (up to 0.08 mg/g). The cinnamaldehyde content was 38.7 mg/g – C. cassia, 19 mg/g –  species of unknown origin and 9 mg/g – C. verum. The cinnamaldehyde-to-coumarin content ratio was highly  differentiated. In the case of the samples with unknown origin that ratio was below 10, and the reference samples  were characterised by a ratio 157 ÷ 680. It was proved, that on the Polish market it was Cassia cinnamon, that was  predominantly marketed as a low-cost spice with no producer’s declaration of its botanical origin.