Silver nanowire (AgNW) networks are a promising candidate to replace indium tin oxide (ITO) as transparent conductors. In this paper, a novel transparent composite conductor composed of AgNW/biocompatible alginate gel on a flexible polyethylene terephthalate (PET) substrate, with synchronously enhanced adhesion and reduced resistivity, is prepared without high-temperature annealing. The sheet resistance of the flexible AgNW/PET film reduces from 300 to 50.3 Ohm sq(-1) at transmittance of 94%. The optical and electrical performance is superior to that obtained from the flexible ITO film on PET. Meanwhile, the sheet resistance does not show great change after tape test, suggesting a good adhesion of AgNW to the polymer substrate. Moreover, the AgNW composite film shows a good stability to resist long-term storage, solvent damage, and ultrasonication. Finally, polymer solar cells employing the composite AgNW film as the electrode are realized, displaying an efficiency of 2.44%.