The natural gabbro samples were deformed at temperature ranging from 700 to 1150 °C with strain rate steps of 1 9 10-4, 2.5 9 10-5, 6.3 9 10-6s-1. The mechanical data show that sample experiences gradual transition from semi-brittle flow to plastic flow, corresponding to a systematically decreasing stress exponent n with the increasing temperature ranging from 16.5 to 4.1(He et al.Sci China(D) 46(7):730–742, 2003). We investigate microstructures and deformation mechanisms of experimentally deformed gabbro under transmission electron microscope in this study. For low temperature of 700 °C to950 °C, the deformation is mainly accommodated with dislocation glide and mechanical twinning, corresponding to stress exponent lager than 5, which means semi-brittle deformation. Whereas with higher temperature up to 1000°C–1150 °C, the deformation is accommodated mainly with dislocation glide and climb corresponding to stress exponent of 4.1, which means plastic deformation. Evidence of dislocation climb has been found as dislocation walls in plagioclase. The observed slip system in plagioclase is(001)1/2[110] and that in clinopyroxene are(100)[001] and(010)[001]. The(010)[001] slip system in clinopyroxene is newly found in this work. Melt was found at temperature of 950 °C–1050 °C. The melt glass distributed both in melt thin film between two grain boundaries and melt tubules of triangular along three grain boundaries at temperature of 950 °C–1000 °C. The melt triangular interconnected to the melt film at temperature of1050 °C–1150 °C, where the melt chemical composition differentiated into iron-rich dark dots and silicate-rich matrix. The natural gabbro samples were deformed at temperature ranging from 700 to 1150 ° C with strain rate steps of 1 9 10-4, 2.5 9 10-5, 6.3 9 10-6s-1. The mechanical data show that sample experiences gradual transition from semi-brittle flow to plastic flow, corresponding to a systematically decreasing stress exponent n with increasing increasing period ranging from 16.5 to 4.1 (He et al. Sci China (D) 46 (7): 730-742, 2003) and deformation mechanisms of experimentally deformed gabbro under transmission electron microscope in this study. For low temperature of 700 ° C to 950 ° C, the deformation is mainly accommodated with dislocation glide and mechanical twinning, corresponding to stress exponent lager than 5, which semi- Whereas with higher temperature up to 1000 ° C-1150 ° C, the deformation is accommodated mainly with dislocation glide and climb corresponding to stress exponent of 4.1, which means plastic deformation. Evidence of di slips climb has been found as dislocation walls in plagioclase. The observed slip system in plagioclase is (001) 1/2 [110] and that in clinopyroxene are (100) [001] and (010) [001] [001] slip system in clinopyroxene is newly found in this work. Melt was found at temperature of 950 ° C-1050 ° C. The melt glass distributed both in melt thin film between two grain boundaries and melt tubules of triangular along three grain boundaries at a temperature of 950 ° C to 1000 ° C. The melt-based interconnected to the melt film at a temperature of from 1050 ° C to 1150 ° C, where the melt chemical composition differentiated into iron-rich dark dots and silicate-rich matrix.