A symmetry analysis of the monoclinic (space group C2/c) Pd6B superstructure formed in the cubic (with structure B1) boron solid solution PdBy in palladium has been performed. The formation of this superstructure occurs as a firstorder phase transition via the disorder–order transition channel including nine nonequivalent superstructure vectors of four stars {k10}, {k4}, {k3}, and {k0}. For the monoclinic (space group C2) Pd6B superstructure, the distribution function of boron atoms has been calculated and the interval of admissible values of longrange order parameters has been determined. It has been shown that the found transition channel is identical to the channel of the formation of the monoclinic (space group C2/c) M6X superstructure; therefore, the Pd6B superstructure can be described with the same accuracy in space group C2. The higher symmetry of the monoclinic (space group C2/c) model suggests that it more accurately describes the structure of the phase Pd6B (Pd6B5) and mutually inverse phases M6X5 and M6X5 than the model with space group C2. It has been demonstrated that there are two types of the nearest environment of metal atoms with nonmetal sublattice sites arranged in the first and second coordination spheres in M6X5 type superstructures (space groups C2/c, C2, C2/m, and P31) and in inverse M6X5type superstructures with the same space groups.