Cellular fatty acids of Erwinia species in the Amylovora group (E. amylovora, E. nigrifluens, E. quercina, E. rubrifaciens, E. salicis and E. tracheiphila), grown on King's medium B agar for 1,3, and 6 days at 28°C, were analyzed by gas‐liquid chromatography, grouped by chemical class, and compared in order to differentiate the species. For the group in general, the average percentage in 1‐day‐old cells ranged 36.4–41.5% for the saturated straight‐chain even‐carbon fatty acids, (Class A), 0.3–0.7% for saturated straight‐chain odd‐carbons (Class B), 43.4–53.3% for unsaturated acids (Class C), 4.5–7.1% for hydroxy‐substituted acids (Class D), 0.2–2.0% for branched‐chain acids (Class E), and 0–7.5% for cyclopropane fatty acids (Class F). Species could be differentiated in 4 sequential steps based on: 1) percentage of the 12:0 fatty acid (E. amylovora >3.6%, E. quercina (1%);2) sum of Classes E + F (E. tracheiphila (0.3%);3) ratio Class A/(E + F) (E. salicis <8); and percentage of 18:1 (E. rubrifaciens >14%, E. nigrifluens < 14%). Physiological age significantly affected relative percentages of Classes B, C and F in E. amylovora and E. salicis; of Classes A, C and F in E. quercina; of Class A in E. tracheiphila; and of Class C in E. nigrifluens.