A complete solid solution of m-Li(Mn1-xCox)BO3 has been successfully synthesized for the first time with the idea of improving the average potential versus m-LiMnBO3. These compounds have been obtained by a multiple-step process. Interestingly, transmission electron microscopy results indicate that the C2/c space group previously reported for m-LiMBO3 (M = Mn, Co) cannot describe m-Li(Mn(1-x)Cox)BO3 compounds. Each material shows electrochemical activity, without in situ carbon coating. Despite a large polarization, we report a capacity of almost 60 mAh/g at the first discharge at C/20 rate with good stability up to five cycles for LiMn0.7Co0.3BO3.