Context : SNR G65.2+5.7 is one of few supernova remnants ( SNRs ) that have been optically detected .
It is exceptionally bright in X-rays and the optical [ O III ] -line .
Its low surface brightness and large diameter ensure that radio observations of SNR G65.2+5.7 are technically difficult and thus have hardly been completed .

Aims : Many physical properties of this SNR , such as spectrum and polarization , can only be investigated by radio observations .

Methods : The \lambda 11 cm and \lambda 6 cm continuum and polarization observations of SNR G65.2+5.7 were completed with the Effelsberg 100-m and the Urumqi 25-m telescopes , respectively , to investigate the integrated spectrum , the spectral index distribution , and the magnetic field properties .
Archival \lambda 21 cm data of the Effelsberg 100-m telescope were also used .

Results : The integrated flux densities of G65.2+5.7 at \lambda 11 cm and \lambda 6 cm are 21.9 \pm 3.1 Jy and 16.8 \pm 1.8 Jy , respectively .
The power-law spectrum ( S \sim \nu ^ { \alpha } ) is well fitted by \alpha = -0.58 \pm 0.07 from 83 MHz to 4.8 GHz .
Spatial spectral variations are small .
Along the northern shell , strong depolarizion is observed at both wavelengths .
The southern filamentary shell of SNR G65.2+5.7 is polarized by as much as 54 % at \lambda 6 cm .
There is significant depolarization at \lambda 11 cm and confusion with diffuse polarized Galactic emission .
Using equipartition principle , we estimated the magnetic field strength for the southern filamentary shell to be between 20 \mu G ( filling factor 1 ) and 50 \mu G ( filling factor 0.1 ) .
A faint HI shell may be associated with the SNR .

Conclusions : Despite its unusually strong X-ray and optical emission and its very low surface brightness , the radio properties of SNR G65.2+5.7 are found to be typical of evolved shell-type SNRs .
SNR G65.2+5.7 may be expanding in a pre-blown cavity as indicated by a deficit of HI gas and a possible HI-shell .