Two red supergiant star S Per and VX Sgr were observed in the OH 1612 and 1667MHz maser lines with the Nancay radio telescope at several runs in 2002-2005 and 2002-2008, respectively. Both targets were sampled at irregular intervals of 2-3 days up to 4 months. Time series of OH spectra in the Stokes parameters I, Q, U and V are presented. The spectra of the linearly polarized flux density, p=sqrt{Q^2^+U^2^}, the degrees of circular polarization, m_C_=V/I linear polarization, m_L_=p/I, and position angle, {chi}=0.5xtan^-1^(U/Q), drived from the Stokes parameters are also given. The degrees of polarization at 1667MHz show diverse behaviours usually uncorrelated with the total flux, whereas those at 1612MHz are commonly stable on time scales of 4-6yr. Several outbursts of the 1667MHz emission on time scales of 0.5-2yr were found in both targets. The bursting features are highly polarized and show drifts in velocity. Small changes of the degrees of polarization and smooth variations of position angle of linear polarization during the bursts were observed in S Per but they are more dramatic in VX Sgr.