A new method for the prepn. of Mn311B7O13I powder sample, used for neutron diffraction, is presented. Magnetization measurements on powder samples of Mn3B7O13X (X = Cl, Br, I) have shown that their Neel temps. are 11 ± 0.5 K for Mn3B7O13Cl, 14 ± 0.5 K for Mn3B7O13Br and 26 ± 0.5 K for Mn3B7O13I. The crystal and the magnetic structures of Mn3B7O13I were investigated by neutron diffraction. The neutron diffraction pattern in the paramagnetic phase at 35 K was refined in space group Pca211'. The neutron diffraction data confirm the onset of magnetic ordering at 26 K. The magnetic structure was detd. at 1.5 K in the magnetic space group Pc'a21'. The magnetic moments of the 3 Mn sites order with a 2D canted spin arrangement. The moments of 2 sites point along c with μz(Mn2) = μz(Mn3) = 3.8(2) μB/atom while the Mn(1) site has a magnetic moment of 5.4(2) μB/atom located in the (101) orthorhombic plane, forming an angle of 12.0(3) degrees with the a direction. The effect of the antiferromagnetic/ferromagnetic compromise on the Mn-I-Mn pathways is discussed.