Abstract. A negative magnetoresistance (NMR) reaching maximum 30-40 % of its zero-field value is observed under in-plane magnetic field in wide Ge1-xSix/Ge/p-Ge1-xSix quantum wells (QW) containing quasi-two-dimensional hole gas, while in an analogous narrow QW the changes of magnetoresistance doesn’t exceed 1 %. In the QWs of intermediate widths and hole densities, the NMR is explained as being caused by suppression of the intersubband scattering due to the upper subband depopulation. In the widest QWs with the highest hole densities the hole gas is self-divided into two 2D sublayers. A similar NMR observed in these samples is tentatively interpreted as also been due to suppression of the intersubband scattering, but subbands are the lowest symmetric and antisymmetric states of the formed double quantum well structure. The main effect of the in-plane magnetic field in this case is a relative horizontal shift of these subbands along the wave vector, rather than the vertical shift in energy.