To provide a backlash preventive material and a method of preventing backlash, which can correspond to the size of an opening freely and have high workability and excellent profitability.

The backlash preventive material contains asphalt of 30-45 pts.wt., an organic solvent of 10-25 pts.wt., a fiber raw material of 5-15 pts.wt. and an inorganic filler of 65-160 pts.wt. A content ratio is represented by pts.wt., and materials excepting the above component may also be comprised, but the backlash preventive material is composed substantially of asphalt, the organic solvent, the fiber raw material and the inorganic filler. The backlash preventive material is not dispersed and the integrality of the backlash preventive material can be maintained because the fiber raw material is contained, and stickiness peculiar to asphalt can be inhibited and the backlash preventive material is handled easily because the inorganic filler is comprised.