A variety of t-butylgermacyclohexanes was prepared and their 13C and 73Ge (when possible) NMR spectra were determined. It was estimated that the conformational energy of a t-butyl group bonded to germanium is about 1.3 kcal mol−1 by NMR data though the molecular mechanics calculations gave variable results depending on the parameter for germanium used; 0.33 kcal mol−1 by Allinger’s parameter while 1.23 kcal mol−1 by Ouellette’s parameter. The origin of this discrepancy was discussed. The molecular orbital calculations (MNDO) gave an intermediate value (0.60 kcal mol−1).