The disclosure describes plastic formed products comprising:one selected from the group consisting of a thermoplastic resin and a thermosetting resin; and0.1 to 10 wt % of at least one selected from the group consisting of ferric oxide hydroxide particles, hematite particles, magnetite particles and maghemite particles;wherein (1) the average major axial diameter or the plate diameter of said ferric oxide hydroxide particles is 0.02 or 2.0 .mu.m and the average aspect ratio or the plate ratio thereof is 2 to 20, (2) the average particle size of said hematite particles, magnetite particles and maghemite particles is 0.01 to 1.0, the BET specific surface area thereof is 1 to 120 m.sup.2 /g and the water content on the surfaces thereof is not less than 0.02 wt %/m.sup.2 /g.