Molecular dynamics simulations are carried out to study flow of Ar around a nanoscale (Pt(FCC (100))) circular cylinder at a low Reynolds number (Re=20) with standard Lennard-Janes potential. Appearance, periodic shedding and oscillation of vortices are shown with streamlines and velocity vectors. Periodic time is about 0.3 ns and Strouhal number is about 0.2. Length of time-average vortices is 1.4 times larger than diameter of the cylinder. Velocity distribution in characteristic regions and recirculation region are obtained.