In this paper dislocation microstructures of olivine xenoliths in vitrobasalt from Dayangke, Mingxi County, Fujian Province are studied by means of tran- smission electron microscope, and the result shows that there are several kinds of dislocations in the mantle-derived olivine, such as dislocation walls, free dislocations, dislocation bows and dislocation loops. These dislocation micros- tructures resulted from complex creep of olivine in the process of high tempe- rature plastic flow in upper mantle. Different types of dislocations indicate different phases of plastic deformation that host minezals expezienced. Based on average free-dislocation density of mantle-derived olivine(2.0 × lO8cm-2) and chemical composition of pyroxene associated with olivine in mantle xeno- liths, it is estimated that the deformation of mantle-derived xenoliths in Da- yangke vitrobasalt took place under the following conditions: temperature (T) 1070℃, pressure(P)2480MPa; depth (Z) 79.3 km, stress(σ1-σ3)136 MPa, flow strain rate(ε)7.6×10(-13)s(-1), and viscosity(η为0.8×10(20)poise.