Thinking is one of the factors of decision making. When the factor is in positive way it will lead the students towards better decision making. The main objective of this study is to find out the association between thinking styles and decision making ability of XI grade students. Thinking Style Inventory constructed by Sternberg (2007) and Decision Making Ability Scale developed by the investigator (2015) are used to collect the relevant data. The sample consisted of 250 XI grade students of whom 106 are male and 144 are female. The data are analyzed using 't' test and chi-square test. The result indicates that there is no significant association between thinking styles and decision making ability of XI grade students.