We have investigated the effect of magnetic field on the low-temperature heat capacity C p of the quasi-1 D compound blue bronze Rb 0.3 MoO 3 , characterized by a charge density wave (CDW) ground state. Below 1 K, C p is dominated by a quasi-linear term, γ T , characteristic of the disordered state of the CDW. Under applied field (between 0 and 2 T), there is an increase of the amplitude γ with H, and simultaneously a downward deviation from the linear regime occurs at an increasing crossover temperature. This could be due to the opening of a (pseudo)-gap in the corresponding spectral density of excitations, which develops with increasing magnetic field.