The identity and rate constants of elementary steps in primary reactions of oxidative coupling of methane (OCM) over Pb 2+ and/or Fsubstituted hydroxyapatite (HAP, Pb-HAP, HAP-F, and Pb-HAP-F) catalysts have been studied. The rigorous kinetics analysis suggests that HAP and HAP-F initiated the reaction between adsorbed methane and O 2 following Langmuir-Hinshelwood behavior. The Pb-HAP and Pb-HAP-F, however, enabled the reaction between gaseous methane and adsorbed O 2 in the Eley-Rideal mechanism. The Fsubstitution of OHweakened both O 2 adsorption and C-H bond activation, leading to low methane conversion and slightly higher C 2 H 6 selectivity. The substitution of Ca 2+ by Pb 2+ weakened both methane and oxygen adsorption, but maintained C-H bond activation and raised C 2 H 6 selectivity. The present analysis explored for the first time the effects of cation and/or anion in HAP on OCM reactions in which the analysis has been detailed and quantified in the nature of the mechanism-based kinetic models.