In this study, we report a large-scale and facile synthetic method for silver nanoparticles via a microwave method, which is quite time-saving and efficient. The obtained silver nanoparticles maintained a uniform size, and the average size was less than 20 nm although the concentration of the silver source was very high. The obtained silver nanoparticles could be homogeneously dispersed in deionized water, which was beneficial for the fabrication of the conductive ink. For large-scale industrialization, the synthetic process window was widened to a great extent via a series of experiments. We injected the ink into a blank mark pen to fabricate a conductive pen, via which the tracks drawn on the photo paper could immediately become conductive at room temperature with an electrical conductivity of 2.4 μΩ cm (about 1.5 times that of the bulk Ag). The mechanical properties of the tracks were examined for a twistable application. After bending at a radius of 4 mm and 2 mm for 5000 circles, only a slight increase in their resistance of 1.20 and 1.78 relative to their initial resistance, respectively, was observed. The as-prepared conductive ink and fabricated pen have potential applications in flexible electronics.