Plectin is a 500-kDa cross-linking protein that plays important roles in a number of cell functions including migration and wound healing. We set out to characterize the role of plectin in mechanical properties of living cells. Plectin−/− cells were less stiff than plectin+/+ cells, but the slopes of the two power laws in response to loading frequencies (0.002–1,000 Hz) were similar. Plectin−/− cells lost the capacity to propagate mechanical stresses to long distances in the cytoplasm; traction forces in plectin−/− cells were only half of those in plectin+/+ cells, suggesting that plectin deficiency compromised prestress generation, which, in turn, resulted in the inhibition of long distance stress propagation. Both plectin+/+ and plectin−/− cells exhibited nonlinear stress-strain relationships. However, plectin+/+ cells, but not plectin−/− cells, further stiffened in response to lysophosphatidic acid (LPA). Dynamic fluorescence resonance energy transfer analysis revealed that RhoA GTPase proteins were activated in plectin+/+ cells but not in plectin−/− cells after treatment with LPA. Expression in plectin−/− cells of constitutively active RhoA (RhoA-V14) but not a dominant negative mutant of RhoA (RhoA-N19) or an empty vector restored the long distance force propagation behavior, suggesting that plectin is important in normal functions of RhoA. Our findings underscore the importance of plectin for mechanical properties, stress propagation, and prestress of living cells, thereby influencing their biological functions.