The expression of interleukin-11 (IL-11) and its products STAT3 and phospho-STAT3 (p-STAT3) in patients with chronic superficial gastritis (CSG), chronic atrophic gastritis (CAG), and gastric cancer (GC) may provide insight into the diagnostic role of the IL-11/STAT3 signaling pathway in GC. Gastric mucosa specimens and serum samples were collected from 90 patients with CSG, CAG, and GC (30/group). The expression of IL-11, STAT3, and p-STAT3 was detected via immunohistochemistry and western blot. Additionally, serum levels of IL-11 were measured by enzyme-linked immunosorbent assay. For IL-11, 60% stained positive in CAG and 83.3% stained positive in GC, which were both higher than the value observed for CSG (33.3%). Moreover, the percent positive for IL-11 in GC was higher than that in CAG (P < 0.05). The percent positive for STAT3 in CAG (80%) and GC (83.3%) was higher than that in CSG (53.3%) (P < 0.05). Compared with CSG (36.7%), the percent positive for p-STAT3 in CAG (63.3%) and GC (86.7%) was also significantly higher. STAT3 expression was similar in GC and CAG, which was significantly higher than that in CSG. Expectedly, p-STAT3 expression gradually increased from CSG to CAG to GC. Furthermore, p-STAT3 levels were higher in GC tissues than in CAG (P < 0.01). Intriguingly, serum IL-11 levels gradually increased from CSG to CAG to GC, which coincided with disease severity. Together, these results suggest that the IL-11/STAT3 signaling pathway plays a critical role in human CAG, and may provide new targets to prevent and treat GC.