To produce the subject yarn having natural uneven feeling with small light and shade color differences, excellent in properties for passing higher-order processes, and useful for a fabric or the like by keeping an average moisture content of a polyamide-based multifilament undrawn yarn at a value lower than a prescribed value, and subjecting the obtained undrawn yarn to a draw- false twist texturing under a specified condition.

A polyamide-based multifilament undrawn yarn obtained by melt-spinning is subjected to a humidity control at ≤25°C in ≤55% relative humidity for 24 hr to keep the average moisture content so as to be ≤4% and the moisture-regulated undrawn yarn is subjected to a draw-false twist texturing in a drawing ratio of the equation [drawing ratio] = 1 + ([elongation at a constant tension-elongation region] × K)/100 (0.6≤K≤1.6) at 50-200°C heat-set temperature, to provide the objective thick-and-thin polyamide-based multifilament yarn. Preferably, the false-twisting is carried out by using a fluid- turning nozzle 3 utilizing a compressed air.