Magnetoresistance (MR) is defined as the relative change in the compound electrical resistivity upon application of an external magnetic field. It is the fundamental property on which important sensing systems and other electronic devices such as computer magnetic random access memories are based.Very large negative magnetoresistance, named Colossal Magnetoresistance or CMR, is observed in three-dimensional oxides like La1-xBaxMnO3 and sulphides like FeCr2S4. However, only a small magneto-resistive effect had been reported in lower-dimensional compounds, i.e. MR ~ 0.8 % in the one-dimensional sulphide BaTi1−xVxS3.We have recently reported a decrease of magnetoresistance from -1.7% to -9% via substitution of the diamagnetic cation Zn2+ for Co2+ in Ba2CoS3. This phenomenon has not been observed before and its origin is still unknown.