The wing rock induced by a hemisphere-cylinder forebody was investigated experimentally using an isolated delta wing and wing body. For the delta wing with sweep angle of 30 deg, no apparent limit-cycle wing rock occurs at angles of attack of 0-90 deg. The mean roll angles exhibit nonzero values at angles of attack of less than 15 deg and become zero at angles of attack of more than 15 deg. For the wing body with a hemisphere-cylinder forebody, apparent wing rock exists at angles of attack of 0-90 deg; the wing rock is induced by the forebody. The phase diagrams showed that the wing rock motion is a typical limit-cycle oscillation at lower and moderate angles of attack. With increasing angles of attack, however, stochastic components in wing rock motion are increased gradually, and the motion types start to deviate from a limit-cycle oscillation. The phase-locked particle-image-velocimetry measurements for the wing body revealed that the vortex pair over the forebody exhibits apparent dynamic hysteresis in position and strength during wing rock, and the dynamic hysteresis of forebody vortices further influence flowfields over the wing, resulting in asymmetric distributions of wing flow, which provides the driving moments sustaining the wing rock.Nomenclature D = diameter of cylindrical body, mm L = span length of wing, mm I = I∕ρL 5 , nondimensional moment of inertia about X axis p = _ ϕL∕U ∞ , nondimensional roll rate Re D = U ∞ D∕ν, Reynolds number based on body diameter U ∞ = freestream velocity, m∕s X = streamwise coordinate, mm α = angle of attack, deg ν = kinematic viscosity coefficient of air, m 2 ∕s ρ = density of air, kg∕m 3 ϕ = roll angle, deg ω = ωL∕U ∞ , nondimensional vorticity