The ferromagnetoelec. boracite Co3B7O13Cl was investigated on (111) cubic cut single crystal platelets in its low-temp. monoclinic ferroelec./ferroelastic/weakly ferromagnetic phase. These platelets were electroded and poled by a thermal process or by the application of a high enough elec. field to get a "ferroelec./ferroelastic nearly single domain" with polarization along the (111)cub direction perpendicular to the platelets. Magnetoelec. measurements were performed on these platelets at 1.5-40 K and up to an applied magnetic field of 10 kOe. The induced polarization, at a d.c. magnetic field of 0.5 kOe, which is proportional to the coeff. of the linear magnetoelec. effect, shows an anomaly at ≈11.3 K. With further increase in temp., a sharp change at nearly 12 K corresponding to the Neel temp. was obsd. The coeff. α32 of the linear magnetoelec. effect, measured quasi-statically at 4.2 K, is ≈13 ps/m (∼3.9 × 10-3 in Gaussian units). The ferromagnetic domain switching with the angular variation of magnetic field is consistent with the monoclinic Shubnikov point group m. The coercive field as a function of temp. measured magnetoelec. shows an exponential behavior.