Microbial (MO), borage (BO) and evening primrose (EPO) 5% (wt/wt) oils were supplemented to a diet consisting of meadow hay and ground barley (60:40) for six days following a five-day adaptation period in an artificial rumen (Rusitec) inoculated with sheep rumen fluid having an A-type ciliate population. After the adaptation period, the following rumen ciliate genera and species were established: Entodinium spp., Dasytricha ruminantium, Eremoplastron bilobum, Diploplastron affine, Polyplastron multivesiculatum and Isotricha spp. (I. prostoma and I. intestinalis). The total ciliate population as well as the population of Eremoplastron decreased (P < 0.05 and P < 0.01, respectively) in the group supplemented with BO. In contrast, the population of Polyplastron increased (P < 0.01) following BO supplementation. The populations of Dasytricha, Eremoplastron, and Isotricha spp. decreased (P < 0.01) in the group with EPO supplement, in contrast to the population of Entodinium spp., which increased (P < 0.05). MO supplementation decreased the populations of Eremoplastron and Isotricha spp. (P < 0.01). None of the oil supplements influenced the population of Diploplastron. The results of this study showed that the examined species of rumen ciliates had no uniform response to the tested oils. Responses strongly depended on the composition of oils and the resultant concentration of the main fatty acid components.