In basic study, pyrolysis of waste thermoplastics (high-density polyethylene (HDPE), low-density polyethylene(LDPE), polypropylene(PP) and polystyrene(PS)) into liquid product was carried out in a stirred semi-batch reactor at atmospheric pressure, under nitrogen stream. Liquid yield in all samples was above 80% and their cumulative amount distribution was influenced by plastic type. For pilot plant of 1 ton/day capacity, the continuous pyrolysis process of mixed plastic waste has been developed in KIER. The characteristics of this process are the continuous treatment of mixed waste plastics, the automatic non-catalytic process and the minimization of the second environmental pollutant. As a experimental result during a long reaction time, the liquid yield was about 80 wt% and also the boiling point distribution of light oil (LO) and heavy oil (HO) produced was a little higher than that of commercial gasoline and diesel, respectively.