Renal failure is typical chronic kidney disease that required peritoneal dialysis as the primary treatment, but current catheter devices lack functionality to monitor changes in chemical analytes during peritoneal dialysis. Fabrication of miniatured sensing modules with good electrochemical performance in tiny catheter devices is the key to realize the smart monitoring of peritoneal dialysis. In this work, a vertical graphene‐based multiparametric sensing array (VG‐MSA) is developed to continuously measure fluctuations of various analyte concentrations for peritoneal dialysis monitoring. Vertical graphene (VG) electrode with good electrochemical properties serves as the core module in VG‐MSA, allowing the development of miniatured sensing modules with sufficient electrochemical performance. The VG‐MSA enables sensitive and multiplexed measurement of dialysate components like metabolites (reactive oxygen species, uric acid, and glucose) and ions (K+, Ca2+, and H+). The VG‐MSA is demonstrated to effectively detect biochemical signals in peritoneal dialysate in vivo on rat models. The VG‐MSA catheter can be inserted into abdominal cavity, allowing full contact with dialysate for in situ, real‐time, and continuous collection of biochemical information during peritoneal dialysis. The VG‐MSA catheter device offers a valuable tool for monitoring dialysis quality and facilitating treatment adjustments, potentially as a promising platform for high‐quality therapy of renal failure.