The influence of selenite or selenate added to ovine ruminal fluid containing linseed oil (LO) on the profile of fatty acids (FA) was investigated. The ruminal fluid was incubated either alone or with LO or with a combination of LO with either a low or high level of Se. The incubation fluid was analyzed to determine the FA levels. The lower and higher concentration of SeIV in the fluids with the LO revealed negligible effect on the concentration of CLA isomers in the fluid compared with the fluid with LO alone. The addition of a higher amount of SeIV to the fluid containing LO decreased the concentration of CLA. The concentration of c9t11c15C18:3 (cLNA) in the fluids with LO, increased throughout the incubations, although the addition of SeIV or SeVI to the fluids containing LO reduced the increase of the concentration of cLNA compared with the fluid with LO alone. The concentration sum of the C18:1 isomers in the control fluid decreased throughout the incubations, while LO added to the fluid increased the concentration of C18:1. LO added to the fluid, irrespective of the presence of Se, increased the concentration of C18:1 compared with the control fluid and the fluids with Se. The concentrations of C16:0 and C18:0 in the control fluid and the fluids containing Se increased throughout the incubations. The concentration of C18:3n-3 decreased throughout the incubation of the fluids containing LO, irrespective of the presence of Se. LO added to the fluids, irrespective of the presence of Se, increased the concentration of C18:2n-6 compared with the control fluid and the fluids with Se. The higher concentration of Se in the fluid with LO increased the concentration of c5c8c11c14c17C20:5 compared with the control fluid or fluids containing LO. LO added to the fluid, irrespective of the presence of Se, increased concentration of polyunsaturated FA compared with control fluid or fluids containing Se.