1. The effect of dietary pea and addition of organic acid blend (OA) or probiotic (Pro) on performance and caecal microbial ecology of broiler chickens was studied. 2. A growth trial was conducted with 160 Ross 308 female broilers from d 1 to 35 of age. There were 8 treatment groups based on either control (S) or white pea (P). Both S and P were supplemented with OA (Galliacid - fumaric acid, calcium formate, calcium propionate and potassium sorbate coated with plant triglycerides, Vetagro) and or with Pro (LABYuc-Probio - lactic acid bacteria, Saccharomyces cerevisiae and Yucca schidigeri extract, Mifarmex GmbH). 3. Inclusion of peas in the diet increased feed intake and decreased gain:feed ratio in comparison to the control diet. Neither probiotic nor OA supplementations affected broiler performance. 4. The caecal microbiota was characterised in 37-d-old birds by fluorescent in situ hybridisation (FISH) and terminal-restriction fragment length polymorphism (T-RFLP). Total bacterial counts in caecal contents were slightly higher for birds fed the pea diets, but were not affected by OA or Pro supplements. 5. Neither pea nor Pro affected the Lactobacillus/Enterococcus and Streptococcus/Lactococcus counts in caecal contents, whereas OA supplementation slightly increased the Lactobacillus/Enterococcus counts. The composition of the Lactobacillus/Enterococcus population was altered by inclusion of peas as revealed by the T-RFLP patterns. 6. The DNA fingerprint further suggested that the caecal microbiota was dominated by the lactic acid bacterium Streptococcus alactolyticus. 7. In ileal contents, the concentration of short-chain fatty acids (SCFA) was decreased only by Pro supplementation. In caecal contents, the SCFA concentration was higher for birds fed on the pea diets, and increased significantly with Pro supplementation 8. In conclusion, the results indicate that the use of pea and probiotics in broiler feed may stimulate the caecal commensal microbiota (growth and/or activity) to some extent and hence prevent establishment of pathogenic and zoonotic enterobacteria in these segments of the gut.