The interactions between atoms and small metal clusters are of great significance in the exploration of novel bonding mechanism. We present the strong chemisorption abilities of ultrasmall iron clusters interacting with large numbers of hydrogen and oxygen atoms from first-principles calculations. Geometric structures show that, the maximum numbers of the sequential hydrogen (oxygen) chemisorption on Fe-1 to Fe-4 clusters can be 11 to 28 (only 5 to 11). Using ab initio molecular dynamics, different kinds of hydrogen diffusion behaviors are found in the Fe-H systems, and two main types of Fe-O bonds are addressed in the stable Fe-O systems. (C) 2018 Elsevier B.V. All rights reserved.