The best performance of solar cells, based on kesterite single crystals and thin films, with conversion efficiency of up to 12.6% [1] was achieved with materials, lying substantially far from the stoichiomety, especially having a Cu-poor/Zn-rich composition.    Here, we investigate the resistivity and magnetoresistance (MR) of Cu2Zn(SnxGe1-x)Se4 (CZTGeSe) single crystals with x = 1, 0.5 and 0 (marked below as # 1, # 2 and # 3, respectively) in pulsed magnetic fields up to 20 T at temperatures between T ~ 10 320 K. The purpose is to obtain information on the conduction mechanisms, as well as on the microscopic properties of charge carriers. Magnetoresistance of CZTGeSe with x = 0.5 is positive (pMR) in all measured fields of B up to 20 T at any T between ~ 40 320 K, whereas MR of samples with x = 1 and 0 contains a negative contribution (nMR). The dependence of  (T) at B = 0 exhibits an activated character within the whole temperature range, attaining a minimum at x = 0.5. At high temperatures,  (T) can be analyzed assuming the nearest-neighbor hopping (NNH) conductivity over localized states of the acceptor band (AB). Linearization of the plots of ln ( T -1) vs. T-1 has permitted determination of the NNH conduction intervals, Tn ~ 260 – 200 K, 274 – 250 K and 320 – 289 K, as well as the NNH activation energy,  En 70, 33 and 75 meV, for samples # 1, # 2 and # 3, respectively. Violation of the NNH conduction regime with decreasing T has been attributed to transition to the Mott variable-range hopping (VRH) conductivity [2, 3]. The Mott VRH conduction in our samples, indicated by linearity of the plots of ln ( T-1/4) vs. T-1/4 [3], has been found within the temperature intervals of Tv = 120  44 K, 255  120 K and 231 51 K for samples # 1, # 2 and # 3 respectively. In addition, the width, W, of the AB has been calculated with the expression of W - 0.5 k (Tv3T0)1/4 [3], where Tv is the VRH onset temperature on cooling and T0 = 2.31-106 K (# 1), 1.45-104 K (# 2) and 7.83-105 K (# 3) is the VRH characteristic temperature. The values of W 72, 30 and 76 meV have been found close to those of En above. This gives evidence for the position of the Fermi energy, , near one of the AB edges. The pMR law of ln  (B)  B2 is observed in both hopping conductivity regimes above, provided that the nMR contribution is absent or saturated. The joint analysis of (T, B) has yielded the values of the acceptor concentration, N = 4.9, 10 and 2.7 (in units of 1019 cm-3), the density of the localized states g = 0.9, 17 and 1.6 (in units of 1017 cm3 meV-1), as well as the localization radius a = 10.5, 21.5 and 12.6 Å for samples # 1, # 2 and # 3, respectively. In addition, the data of a/a0 = 1.96, 4.35 and 1.93, and those of N/Nc = 0.49, 0.77 and 0.48 for samples # 1, # 2 and # 3, respectively, were obtained, indicating a relative closeness of samples to the metal-insulator transition (MIT). Here, Nc is the concentration of the MIT and a0 is the localization radius far from the MIT. All the parameters above exhibit a non-monotonous dependence on x, including an extremum near the same value of x = 0.5. Such behavior suggests a corresponding systematic variation of disorder and defect concentration in CZTGeSe.  This work was supported by the institutional project and STCU #5985. The authors would like to acknowledge E. Arushanov and M. Guc for fruitful discussions.