The present study suggests the UV-spectrophotometric assay of mediborol in its oil solutions, which is based on the Firordt’s method and does not require previous separation of the active substance from the oil components. The validation data of the developing method showed that the dependence of real content from observed content of mediborol in the concentration range1,6 – 2,4% is linear with correlation coefficients of R² = 0,999 for the solution in peach oil and R² = 0,995 - in the olive. Accuracy is in the range of 98,72 to 100,83% and from 98,64 to 101,11% for mediborol’s solutions in peach and olive oils, respectively. The relative error in determination of mediborol ranges from 2,09 to 2,81%.