The purposes of this study were to select useful questionnaire items when measuring mental toughness in water polo players through an examination of item analysis, and to determine the reliability of reselected items based on Cronbach's α-coefficient. It was assumed that a hypothetical structure of mental toughness consists of 17 sub-domains. A survey composed of 102 items representing each sub-domain (6 items) was administered to competitive water polo players. In the examination results of internal consistency and good-poor analyses, 3 items were eliminated and 99 items were reselected as useful items. Inter-consistency (factor validity) by component analysis and reliability by Cronbach's α-coefficient were examined according to each domain. Although all domains had high reliability coefficients of 0.70 or over, items with a low validity were also confirmed. Next, considering practicability, four items with higher validity were selected from each domain, factor validity and reliability were examined again. It was confirmed that all items have high validity and reliability. Sixty-eight items finally selected are considered to be useful questionnaire items to measure mental toughness of water polo players. From now, it will be necessary to select useful items considering an examination of factorial structure of mental toughness.
