Background. The cannabinoid receptor (CBR) plays a significant role in oogenesis, pregnancy, and childbirth. It might also play a significant role in preterm birth (PTB). The aim of the study was to investigate the association between the expression of the cannabinoid receptor in the placenta and the incidence of preterm birth.Methods. This prospective, observational, multicentre preliminary study was conducted on placental samples obtained from 109 women. The study included 95 patients hospitalized due to the high risk of PTB. They were divided into two groups: Group 1, where the expression of the CBR1 and CBR1a was analyzed, and Group 2, in which we examined CBR2 expression. The control group, i.e., Group 3, consisted of 14 women who delivered at term and their placentas were tested for the presence of all three receptor types (CBR1, CBR1a, CBR2).Results. The study used reverse transcription and Real-Time PCR methods to assess the expression of CBRs in the placental tissues. The expression of the CBR2, CBR1 and CBR1a receptors was significantly lower in the placentas of women after preterm birth compared to those after term births, p = 0.038, 0.033 and 0.034, respectively.Conclusions. The presence of CBR mRNA in the human placental tissue was confirmed. The decreased expression of cannabinoid receptors could serve as an indicator in predicting PTB. KEYWORDS: Cannabinoid receptor; CBR1; CBR2; ECS; preterm birth; PTB.