Ozone is considered a promising food preservation technique and has gained great interest because of its strong oxidizing properties and significant antimicrobial efficacy, and because its decomposition leaves no residue in food. In the present study the combined effect of ozone and citric acid treatment on quality and shelf life of freshly cut lettuce packaged under a passive modified atmosphere during cold storage was investigated. Lettuce were washed, cut and treated with ozone at 0.5, 1.0 or 1.5 ppm for 45 minutes. Another batch was treated with citric acid and 3 additional batches were treated with ozone at the above concentrations plus citric acid. Headspace analysis, color parameters, pH, microbiological and sensory analysis were monitored during cold storage. Carbon dioxide production rates increased significantly (p