An Otto cycle working with an ideal Bose gas is called a Bose Otto cycle. The internal irreversibility of the cycle is included in the factors of internal irreversibility degree. The quantum degeneracy effect on the performance of the cycle is investigated based on quantum statistical mechanics and thermodynamics. Variations of the maximum work output ratio R-W and the efficiency ratio y with temperature ratio T are examined, which reveal the influence of the quantum degeneracy of the working substance on the performance of a Bose Otto cycle. It is shown that the results obtained herein are valid under both classical and quantum ideal gas conditions. (c) 2006 Elsevier Ltd. All rights reserved.