The concepts of Blow molding is a process used to produce hollow objects from thermoplastic. The basic blow molding process has two fundamental phases. First, a parson (or a perform) of hot plastic resin in a somewhat tubular shape is created. Second, compressed air is used to expand the hot perform and  press it against mould cavities. The pressure is held until the plastic cools. Blow molding process is used for which has thin wall sections.In this thesis, blow mould design is to be done for a bottle having 0.5mm thickness. This  thickness cannot be filled in pressure injection molding. So blow molding is considered for pet bottle design. The mould is prepared by first modeling the part, extracting core & cavity and generating CNC program. Blow mould tool design is done in Pro/Engineer according to HASCO standards. A prototype of the pet bottle using blow mould design is also included.