Sweat is a biomarker that contains ions and biochemical compounds that may reflect human health conditions. Wearable biosensors enable the collection and analysis of sweat in situ, noninvasive, real-time, continuous monitoring of biochemical compounds. This paper presents the development and characterization of wearable biosensors for ion detection in sweat. The screen-printed method was used for the fabrication of a working electrode and a reference electrode on cotton fabric. The reference electrode was constructed from Ag/AgCl ink. The working electrode is constructed from a modified carbon electrode, conducting polymer, and an ion-selective membrane. Artificial sweat with known compositions was used for biosensor validation. The biosensors had been used to detect the sodium and potassium ions in sweat from patients with soft activities.