Abstract: Potato is one of the most important food crops after wheat and rice. The effectiveness of lactoferrin against Potato virus x (PVX) in vitro and in vivo have been evaluated. Four concentrations of lactoferrin 100, 250, 500 and 1000 mg L-1 were examined either in vitro culture medium or in vivo (greenhouse). The presence of the virus was evaluated by ELISA technique. Data demonstrated that application of 1000 mg L-1 lactoferrin by spraying or combined with tissue culture proved to be an effective method for PVX-inhibition as compared with other concentrations. Also, results of antiviral activity of lactoferrin at concentration 1000 mg L-1 showed great potential as phytotherapeutic source to produce quality and health plantlets for rapid and large scale in vitro production. Lactoferrin seemed to be very successful and inexpensive in controlling viral infection through in vitro technique or by spraying the infected and/or healthy plant under greenhouse condition.