Provided is a throttle valve assembly which reduces weight, number of manufacturing processes, and manufacturing cost thereof by coupling a throttle body formed of plastic to a reinforcement portion manufactured by a die casting method with an insert method. The throttle valve assembly includes a valve body having an intake passage, a mounting space that communicates with the intake passage, a motor accommodating space, and a mounting groove formed between the mounting space and the motor accommodating space. The valve body includes plastic. The throttle valve assembly further includes a valve plate coupled to a rotary shaft rotatably installed in the intake passage of the valve body to adjust an amount of air or a mixed gas ingested into an engine; and a reinforcement portion formed of a metal and coupled to an inside of the valve body by an insert injection method.