Background/Objectives: Arterial stiffness is a major cardiovascular risk factor in patients with hemodialysis (HD). We conducted a cross-sectional study aimed at determining the relationship between serum p-Cresyl sulfate (PCS) and peripheral arterial stiffness (PAS), defined via the cardio-ankle vascular index (CAVI), in 110 patients receiving chronic HD. Methods: Participants were divided into PAS (CAVI ≥ 9.0) and control (CAVI < 9.0) groups. Serum PCS level was measured by high-performance liquid chromatography-mass spectrometry. Results: PAS was detected in 37 (33.6%) patients. The PAS patients were older and had higher SBP, more diabetes, and higher serum PCS and C-reactive protein (CRP) than the control group. Upon multivariate analysis, PAS was significantly associated with PCS (adjusted odds ratio: 1.238 per 1 mg/L increase, 95% confidence interval [CI]: 1.119–1.371, p < 0.001). The CAVI, advanced age, and CRP demonstrated a significant correlation with PCS, as evidenced by the correlation analysis conducted. Area under the receiver operating characteristic curve analysis showed that PCS had a good diagnostic value for PAS (AUC: 0.872, 95% CI: 0.805–0.939; p < 0.001), and the optimal cutoff value was 24.29 mg/L. Conclusions: PCS demonstrates great potential as a biomarker in the diagnosis of arterial stiffness.