Paper packaging materials are essential in protection and transportation of commercial or industrial products. Raw materials for packaging paper production are mainly obtained from various grades of waste paper. For this reason, the recycled fibers from waste paper would probably have possibility of containing heavy metals. This study was focused on the development of optimum pre-treatment method for the quantitative analysis of mercury. The optimum pre-treatment for open digestion system were obtained at the treatment conditions of acid combination with $HNO_3/HCl/H_2O_2$ or $HNO_3/H_2SO_4$ at $80^{circ}C$. The optimum pre-treatment conditions in closed digestion system were determinated by the acid combination with $HNO_3/HCl/H_2O_2/HF$ in microwave at 320 W for 20 min. The recovery rate in open digestion system was 85~94% and in closed digestion system was indicated as about 100%. Therefore, the closed system is superior than the open system in pre-treatment method for the quantitative analysis of mercury, and the detected mercury contents in the sample of KOCC, AOCC and kraft sack paper were measured below 1 ppm.