The heterotrimeric transmembrane lymphotoxin ${alpha}1{eta}2$ ($LT{alpha}1{eta}2$), member of the tumor necrosis factor family cytokines including soluble homotrimeric lymphotoxin ${alpha}$ ($LT{alpha}$), plays an important role in lymphoid tissue architecture and organogenesis. We found that lymphotoxin ${eta}$ receptor ($LT{eta}R$) stimulation using agonistic anti-$LT{eta}R$ antibody induced the changes in actin stress fiber and morphology of cells. To address the possibility that $LT{eta}R$ stimulation is involved in RhoA/Rho-associated protein kinase (ROCK) signaling, we checked the level of Rho-guanosine diphosphate (GDP)/guanosine triphosphate (GTP) exchange activity with fibroblastic reticular cell (FRC) lysate. When $LT{eta}R$ was stimulated with agonistic anti-$LT{eta}R$ antibody, the Rho-GDP/GTP exchange activity was markedly reduced. Inhibition of ROCK activity induced changes in actin cytoskeleton organization and cell morphology in FRC. We showed that the phosphorylation of myosin light chains (MLCs) was reduced by $LT{eta}R$ stimulation in FRC. DNA gene chip demonstrated that agonistic anti-$LT{eta}R$ antibody in FRC affected the downregulation of actin filament and myosin component transcripts. The results provided here indicated that RhoA/ROCK was responsible for the observed phosphorylation of MLC. Collectively, these results suggest that $LT{eta}R$ stimulation is involved in change of stress fiber via RhoA/ROCK signaling in FRC.