This study aimed to investigate the effect on the severity and prognostic value of serum procalcitonin for elderly patients with oral and maxillofacial infections. We divided 163 elderly patients with severe oral and maxillofacial infection into survival and death groups according to the prognosis between June 2015 and May 2021, measured serum procalcitonin by enzyme-linked immunosorbent assay on the 1st, 2nd, 3rd, 5th, and 7th day after admission for the dynamic changes of serum procalcitonin level, collected the general physiological and biochemical indexes for the scores of acute physiology and general chronic condition, compared the correlation between serum procalcitonin, mean platelet count and APACHE score, analyzed the prognostic value of serum procalcitonin levels at different time after admission by ROC curve. The serum procalcitonin level increased significantly in both groups after admission, sharply increased at first and then rapidly decreased in the survival group, and continued to rise or declined slowly with fluctuation of high level in the death group. There was a negative correlation between serum procalcitonin level and mean platelet count (r = −0.698, P < .05) and a positive correlation between serum procalcitonin and APACHE II (R = 0.803, P < .05). The ROC curve showed that the serum procalcitonin level had little value on the first day and great value on the third day in predicting the prognosis of elderly patients with severe oral and maxillofacial infection (PCT1d = 0.539, PCT3d = 0.875, P < .05). The serum procalcitonin level is correlated with the severity of the disease in elderly patients with severe oral and maxillofacial space infection. Dynamic observation of it is helpful for the prognosis judgment of patients. After admission, serum procalcitonin level on the third day has a great value for the prognosis judgment of elderly patients with severe oral and maxillofacial space infection.