St. Johns wort (Hypericum perforatum) is a medicinal plant that exhibits important biological activities exhibit important biological activities being antioxidant, anti-inflammatory, immunomodulatory and/or antitumour. The aim of this study was to investigate antiproliferative effect of H. perforatum oil purchased from a commercial vendor on mouse myeloma cells. The cells were treated with various concentration (10%, 5%, 2%, 1%, 0.5%, 0.25%, 0.2% and 0.1%) of dimethyl sulfoxide (DMSO) to determine the non-toxic concentration. The cells were treated with various concentrations (15.6-500 ppm) of the oil dissolved in DMSO to examine its antiproliferative activity. Non-toxic dose of DMSO was at the concentration of lower than 0.2%. No effect on the cell proliferation was observed in the applied concentration of the oil. In conclusion, the oil had no antiproliferative effect on Myeloma cells at these concentrations.