We have investigated the electrical properties of rock sample from Yinshan orogenic zone by in situ complex impedance spectroscopy using a multianvil apparatus. The electrical conductivity was measured at pressure of 1 GPa and temperature from 250 ℃ to 1 100 ℃ at frequencies from 0.1 Hz to 1 MHz. The data of resistance were obtained by using an equivalent circuit fitting technique. From these measurements we determined the electrical conductivity of the Archean metamorphic biotite- and plagioclase-bearing gneiss. The experimental results indicate that (1) each spectrum consists of an almost semicircular high-frequency arc Ⅰand a depressed high-frequency arc Ⅱ. The impedance spectrum Ⅰ is dominated by grain-interior response; the impedance spectrum Ⅱ is dominated by the sample-electrode interface impedance. (2) Electrical conductivity displays Arrhenian behavior respectively over investigated temperature range from 250 ℃ to 700 ℃ and from 750 ℃ to 1 100 ℃. However, it rapidly increases from 700 ℃ to 750 ℃. This jump is due to dehydration-melting of biotite within sample based on the comparative analysis of SEM photoes and electron probe data for pre-run and post-run samples. (3) Over higher temperature range (750~1 100 ℃), sodium is the dominating charge carrier in partially molten samples. (4) The activation energy of biotite- and plagioclase-bearing gneiss is 0.53 eV over range of temperature from 250 ℃ to 700 ℃. However, the activation energy of partially molten sample is 1.41 eV over range of temperature from 750 ℃ to 1 100 ℃. This change of activation energy has relations with sodium content and mobility in melt. It is possibly due to the change of structure between mineral and melt within samples.