In order to explore the potential of dielectric properties in determining fruit internal quality, peaches with different maturities were selected and coaxial open-ended probe technology was used to measure permittivity of peach pulp and juice over the frequency range from 10 to 4500 MHz at 25℃. The moisture content of peach pulp, soluble solids content, pH value and electrical conductivity of juice were also measured. The results showed that the dielectric constants of pulp and juice decreased with increased frequency, while the loss factors changed with “V” type. The ionic conduction and dipolar polarization were the major loss mechanisms at lower frequencies and higher frequencies, respectively. The relationship between permittivity and soluble solids content, pH value, and moisture content was non-linear.