In this study, we investigated the effects of Ganoderma lucidum extract (GLE) supplementation on the cecal microbiota of broilers challenged with dextran sulfate sodium (DSS) during the starter phase. A total of 32 one-day-old, unsexed broiler chicks were randomly divided into four dietary treatments with eight birds per treatment and reared individually for 14 days (n = 8). The diet treatments were: non-DSS challenge, DSS challenge only, DSS challenge plus 0.5 mL/L GLE, and DSS challenge plus 1 mL/L GLE. The results showed that DSS challenge plus 0.5 mL GLE alleviated inflammatory gene expression in the duodenum of broilers (p≤0.01). The alpha diversity of bacterial species in the cecal digesta increased in the group treated with DSS plus 1 mL/L GLE compared with the DSS challenge-only group (p≤0.01). Principal component analysis and principal coordinate analysis indicated distinct clusters between groups treated with DSS-only and DSS plus GLE (0.5 and 1 mL/L). The abundance of the genera Ruminiclostridium 9, Enterococcus, and Sellimonas increased in the group treated with DSS plus GLE (0.5 and 1 mL/L) compared with the other groups (p≤0.01). Comparative microbial function analysis demonstrated that the immune system was promoted in the group treated with DSS plus GLE (0.5 and 1 mL/L) compared to the DSS challenge-only group (p≤0.001). These results demonstrated that GLE supplementation can modulate the cecal microbial community of broilers under DSS challenge during the starter phase.