This paper describes plasma acceleration behavior in a pulsed plasma thruster (PPT). A PPT is a form of electric propulsion device in which plasma is accelerated by the interaction between pulse currents and magnetic fields to create thrust. It is one of the most promising electric propulsion devices with the advantages of simplicity and relatively low manufacturing cost. In this study, a prototype solid-fed PPT that produces plasma and accelerates it to a high velocity was designed and demonstrated. This prototype PPT produces an impulse bit of 84 μN．s when 6.25 J of energy is employed. Plasma is a quasi-neutral matter of charged and neutral particles that exhibits a collective behavior. To examine plasma behavior, a triple Langmuir probe was designed to determine the electron density and electron velocity. A plasma density of 8 × 10^(20) m^(-3), 30 mm from a nozzle with a maximum electron velocity of 25 km/s, was observed. In addition, a high-speed camera was employed to visualize the Lorentz force acting on the plasma and the evolution of plasma plume formation in the discharge chamber.