Energy requirements of whole world have been dominated by petroleum products for many years in various application fields. In order to find the potential replacement for conventional mineral oil, natural based ester oil is proposed as alternative liquid insulation with the consideration of eco-friendly nature among ester oil, the oil with oleic acid content has oxidation resistance and low viscous nature. In this work blending of mineral and high oleic ester oil with different ratio were carried out to study the typical characteristics of blended liquid as liquid insulation. Olive oil and rapeseed oil which has high oleic acid content are selected for investigation. Investigation properties like viscosity, breakdown voltage, flash point, acidity, moisture content and moisture saturation rate were measured for different combinations as per international standards (IEC and ASTM). Investigation reveals that both olive and rapeseed based blended oil show better characteristics, among that olive based blended oil have superior properties than that of rapeseed oil.