Single crystals of 4-Bromowuweizichun B, C23H27O7Br, belong to the space group P212121 with four molecules per unit cell. Since both the Y and Z parameters of the bromine atom are close to 1/4, either the heavy atom method or the Patterson method would lead to a four-fold ambiguity for each light atom. Consequently the structure analysis could not proceed by the usual way. By making use of the method proposed by one of the authors, the ambiguity was easily resolved and the correct structure obtained.