This paper reports the first high-performance water-based isotropically conductive adhesives (WBICAs) – a promising material for both electrical interconnects and printed circuits for ultralow-cost flexible/foldable printed electronics. Through combining surface iodination and in situ reduction treatment, the electrically conductivity of the WBICAs are dramatically improved (8 × 10-5 Ω cm with 80 wt% of silver); moreover, their reliability (stable for at least 1440 h during 85 °C/85% RH aging) meets the essential requirements for microelectronic applications. Prototyped applications in carrying light emitting diode (LED) arrays and radio frequency identification (RFID) antennas on flexible substrates were demonstrated, which showed satisfactory performances. Moreover, their water-based character may render them more environmentally benign (no volatile organic chemicals involved in the printing and machine maintenance processes), more convenient in processing (reducing the processing steps), and energy economic (thermally sintering the silver fillers and curing the resin is not necessary unlike conventional ICAs). Therefore, they are especially advantageous for mass-fabricating flexible electronic devices when coupled with paper and other low-cost substrate materials such as PET, PI, wood, rubber, and textiles.