The production process is inseparable from a problem or reject product. PT. XYZ is a flexible packaging converter manufacturing company that has commitment in maintaining quality to reduce reject products. During the period January 2018 - December 2018 the reject value is still above the standard. This study aims to determine the factors causing the reject products of oil pack at PT. XYZ and proposed improvement to control of reject oil pack products. The results of pareto diagram show the reject that gave the biggest contribution is dirty in the printing process, thickness and wrinkle in the lamination process, and saggy in the slitting process. These four factors were analyzed using a fishbone diagram and then propose improvements for the causes of problems with the 5W and 1H methods. The analysis using cause and effect diagrams found that the main causes are the lack of supervision and inconsistency of the operator; poor maintenance of the engine unit; setting machine parameters and order schedules that not precise; the lack of supply and quality of raw materials. And then propose improvements with the 5W1H methods. The proposed improvements are briefing SOP and making engine alarm system; do maintenance, repair or replacement of damaged machine units; setting the machine parameters and order scheduling; monitoring the availability and quality of raw materials. The evaluation results of improvements can reduce the reject in the printing process 45%, the lamination 23% and the slitting 40%.