Abstract: To provide basic data for the developing of moisture content sensors for coarse cereals based on dielectric properties, oat seed samples were used to study the effects of frequency (1-103 kHz), moisture content (12%-21%), temperature (5-40℃) and bulk density (671-787 kg/m3) on the relative permittivity ε′ and dielectric loss factor ε″ by coaxial-line cylinder capacitor. The reasons why permittivity changed with these factors were analyzed. Furthermore, the mathematical models between permittivity of oat seeds and main influencing factors at 103, 104, 5×104, 105, 5×105 and 106 Hz were established and validated. The results indicated that the relative permittivity ε′ and dielectric loss factor ε″ of oat seeds were decreased with the increasing of frequency, and increased with the increasing of moisture content, temperature and bulk density. The relationship between permittivity and main influencing factors can be described by ternary or binary cubic equations, with the coefficients of determination higher than 0.96. Compared with the moisture content obtained from oven drying method, the errors of predicated moisture contents of oat seeds based on dielectric properties at 104, 5×104, 105, 5×105 and 106 Hz were within ±1.2%, and it is feasible to predicate the moisture content of oat seeds based on dielectric properties. The study is helpful to understand the dielectric properties of oat seeds, and is instructive to develop moisture sensor for oat seeds.