The present invention provides a thinned flexible polyimide substrate and a method for manufacturing the same. The thinned flexible polyimide substrate comprises a polyimide resin, a conductor layer, and a polyimide insulating layer. The polyimide resin has a linear thermal expansion coefficient of less than 40 ppm/K. The conductor layer is formed of a plurality of stacked metal nanoparticles having pores therebetween, and each of the pores has a size between 0.1 μm and 1 μm. A portion of the polyimide resin fills into the pores. The polyimide insulating layer is formed of the polyimide resin coated on the conductor layer.