摘要:In this study, the effect of weather on Istanbul Stock Exchange (ISE) for the period between January/11/1987 toDecmber/31/2006 is analyzed. While ISE100 index is used to represent Istanbul Stock Exchange`s return,cloudiness and humidity values are used as weather variables. For the selected period; variance, average andthe hypothesis of medians equality with daily data were tested in the study. While the relationship between theweather variables and stock returns is tested, weak-form efficiency test in ISE is performed at the same time, inthe study. Obtained data support that ISE is not affected by the selected weather variables; thus, there is anefficient market in the weak-form. In other words; developing new investment strategies would not give effectiveresults for ISE and excessive profits cannot be obtained.