Wearable sensor technology is essential to achieve personalized health management via continuous monitoring of individual health status. Although diaper-based biosensors have been developed, multiplex strategies for biomolecular sensing of urine in situ are still rarely investigated, which limits a comprehensive assessment of the wearer's health information from urine. In this study, we present a mechanically flexible and smart diaper based on integrated multiplex electrochemical sensors (MECSs) for in situ urinalysis that simultaneously and selectively measures urinary metabolites (e.g., glucose, reactive oxygen species with H2O2 as an example, and uric acid) and electrolytes, including sodium and potassium ions. The sensor electrode arrays were modified with carbon nanotube coatings and chemical substances (ion-selective membranes, enzymes, or Pt nanoparticles) to achieve highly selective and sensitive monitoring of target biomarkers associated with urine status. The MECSs could be further prepared into a prototype that integrates a biosensor module, flexible circuit board, and Bluetooth signal transmitter to provide a promising substitute for monitoring for bedside patients, infants, and senior citizens.