Background Delayed colectomy can be life-threatening for patients with acute severe ulcerative colitis (ASUC). However, few biomarkers can predict the outcomes of ASUC patients before treatment. Serum procalcitonin (PCT) has been observed to be increased in ASUC patients. Aim The aim of this study was to estimate the association between serum PCT and short-term outcomes in patients with ASUC. Methods A single-center observational study was conducted at a referral hospital from January 2012 to January 2018. Hospitalized ASUC patients, who were administered intravenous corticosteroids (IVCS), were enrolled and followed up for 6 months. The primary outcome was IVCS failure; the secondary outcome was colectomy. Relationships between indicators and clinical outcomes were assessed. Results Of 152 ASUC patients enrolled in this study, 81 responded to IVCS and 71 failed (62 required short-term colectomy and 9 responded to second-line rescue therapy). Serum PCT on admission was significantly higher in IVCS-failure cases and surgical cases than in medical responders. Serum PCT >= 0.10 mu g/L (OR=4.134, p=0.001) predicted IVCS failure with specificity of 0.741, and the combined measurement with fecal calprotectin (FC) >= 1500 mu g/g improved the sensitivity. Serum PCT correlated significantly with the Ulcerative Colitis Endoscopic Index of Severity (r=0.416, p<0.001) and FC (r=0.384, p<0.001). Conclusion Serum PCT on admission could be a potential early non-invasive predictive biomarker for IVCS failure in ASUC patients, and a combination of PCT and FC could improve the predictive value.