The growth behavior of Y1Ba2Cu3O7- x (YBCO) thin films on MgO substrates synthesized by laser ablation deposition techniques has been investigated. The effects of important parameters, i.e., substrate temperature, post annealing schemes, laser beam fluence and deposition chamber atmosphere on the crystal structure microstructure and superconductivity of the deposited films have been studied. Among those important depositing parameters the plume to film interaction was observed to impose the most prominent effect on the film characteristics. The films were found to consist mainly of a noncrystalline phase whenever the substrates were located either in the invisible or the supersonic zones of the plume. Only when the substrates are positioned in the reactive zone does the crystalline phase grow rapidly via a nucleation and growth mechanism. The (013) grains nucleate preferentially and are subsequently transformed into a (00 m) orientation ossibly by diffusion. The number of (013) grains transformed increases with temperature used for step annealing and with time at that temperature.