The present work describes the optically stimulated luminescence (OSL) of a tissue equivalent crystal, the magnesium tetraborate, doped with dysprosium or cerium and co-doped with lithium due to the lack of materials with characteristics suitable for several dosimetric applications. In the present work, MgB4O7:Dy,Li and MgB4O7:Ce,Li were characterized through their OSL and radioluminescence emissions. Our results indicate that MgB4O7:Ce,Li has a strong emission peaked at 420 nm that is connected to the Ce3+ electronic transitions, while the emission of MgB4O7:Dy,Li has several peaks connected to the Dy3+ transitions. The OSL decay curves from both materials are composed by two components: a slow one and a fast one. MgB4O7:Ce,Li is 10 times more sensitive than MgB4O7:Dy,Li, especially due to the wavelengths of the emission peaks. The dose response for both materials were sublinear from 0.2 Gy to 100 Gy, for MgB4O7:Ce,Li, and from 0.2 Gy to 40 Gy, for the MgB4O7:Dy,Li. The OSL signal from MgB4O7:Ce,Li showed good stability over 40 days (with a fading < 1%), while MgB4O7:Dy,Li presented a complete fading of the signal after 40 days. These results suggest a clear potential of MgB4O7:Ce,Li for radiation dosimetry purposes using OSL technique.