This paper presents the basic physical, chemical and electrical properties of a type of rapeseed oil based dielectric liquid. Dielectric properties including relative dielectric permittivity, dissipation factor, and breakdown voltage of the rapeseed oil paper insulation are presented and also compared with those parameters of mineral transformer oil paper insulation. Moreover, four types of small oil gaps are designed for experiments. These four types of oil gaps include a simple oil gap, an oil gap with a paper-covered high voltage electrode, and two oil gaps with one and two layers of papers, respectively, between the high voltage and grounding electrodes. Both the refined rapeseed oil and the mineral transformer oil are used for the small oil gap experiments. Breakdown properties of the small oil gaps are measured. The analysis results of test data show the differences in dielectric properties between the rapeseed oil paper insulation and the mineral transformer oil paper insulation.