The potassium-magnesium salt deposit of Khammouan Province in Laos is located in the eastern part of Khorat Basin. The main salt minerals of the deposit are halite, sylvite, carnallite and anhydrite, and the boron minerals in the deposit are of small or even trace amounts. The identification of trace boron minerals in the lower salt layer of ZK318 borehole in the deposit was studied in order to complete the mineral assemblage type. Chemical analyses show that the content of boron is related to the type of salt minerals, and that according to the distribution characteristics of boron, the lower salt layer can be divided into five layers in upward succession, i.e., halite layer→sylvite layer→carnallite layer→thin halite layer→upper sylvite layer. According to the linear relationship between the content of boron and the salinity of brine, carnallite, as the last evaporative product of halide brine, should have the highest content of boron theoretically. However, the boron value of the upper sylvite layer is up to 890.78×10^-6 which is higher than that of the carnallite layer, indicating that boron in the upper sylvite layer came not only from sea water but also from deep hydrothermal solution and that there exist small amounts of boron minerals in this layer. Preliminary XRD analytical results of bulk rock samples show that there is a small amount of boracite in the upper sylvite layer. In order to identify the type of boron minerals accurately, the authors conducted XRD analysis of insoluble substances collected through the soluble experiment of bulk rock samples. The result shows that the boron minerals in insoluble substances are mainly boracite (55%), and subordinately anorthic hilgardite-3A (15%). Hilgardite-3A belongs to trace mineral because its content is less than the detection limit of XRD (1%) so that there is no diffractive peaks in the XRD pattern of bulk rock samples. In addition, the Chinese name of anorthic hilgardite-3A is discussed in this paper. It is pointed out that the precise Chinese naming should follow the international conventions. Therefore, the name parahilgardite is cancelled and replaced by the name hilgardite-3A so as to reflect the slight difference between the mineral structures, i.e. the difference between this mineral and another anorthic polymorph 1A. This modification is consistent with the Chinese naming norms. Therefore, small amounts of boracite and trace hilgardite-3A (anorthic) exist in the potassium-magnesium salt deposit of Khammouan Province, Laos.