In this paper, the effects of dispatching rules on the scheduling performance of job-shops with different flexibility levels are analyzed. Four different flexibility levels are defined for operations. Five dispatching rules are evaluated according to mean tardiness as the performance criteria for the scheduling system, Performance variations of dispatching rules among different machine flexibility levels are determined and statistically analyzed. It is found out after detailed analysis that the effect of dispatching rule selection on job shop performance weakens as the job shop flexibility increases. This important finding Should be taken into account while designing scheduling systems for job shops that are flexible. (C) 2009 Elsevier B.V. All rights reserved.