Abstract: The piezoresistivity of short carbon fiber reinforced cement-matrix composites (CFRC) was experimentally studied. The whole process of transition from positive to negative piezoresistivity was observed. The results show that under continuously drying and uniaxially cyclic loading, both positive and negative piezoresistivity occur in CFRC due to the variation of moisture content in the composites. For most cases the electrical resistivity of the composites decreases monotonically upon longitudinal compression, and piezoresistivity tends to be positive. However, its magnitude varies. Lower moisture content leads to stronger piezoresistivity. When moisture content reduces to about 3.19%~4.04%, the electrical resistivity of the composites increases monotonically upon compressive strain, and piezoresistivity tends to be negative. This effect is much stronger than that of positive piezoresistivity. It is proposed that the occurrence of these phenomena is attributable to both the tunneling effect between fibers and decreasing in pore network connectivity during compression.