A polyamide masterbatch free from metal copper deposition and metal corrosion in an extruder or a molding machine, deterioration in mechanical physical properties of the product, and a color change of appearance due to water absorption and having improved heat aging resistance is produced by mixing, by melt kneading, a) 100 parts by weight of a polyamide having a water content of from 0.05 to 2.0 wt. %, b) from 0.1 to 10 parts by weight of an organic compound having at least one amide group, c) from 0.1 to 5 parts by weight of a copper compound having a maximum particle size of 50 μm or less, and d) from 1 to 50 parts by weight of a halogen compound (with the proviso that a copper halide is excluded) having a maximum particle size of 50 μm or less.