The Thailand Industries Sentiment Index (TISI) dropped in September due to concerns about a hike of oil prices and the baht's appreciation, the Federation of Thai Industries (FTI) reported on Thursday.
The survey in September showed the index stood at 91.5 points, down from 92.5 in August.
"Most business operators are concerned about oil prices, which hit US$83 per barrel in the global market. They affect the country's overall transportation cost," said FTI chairman Supant Mongkolsuthree.
"The baht strength is now a worrisome issue when compared to the currency movements in Southeast Asia countries," he added.
The FTI foresaw pressure from the prolonged trade war between the United States and China to affect export sentiment but the promised general election will push the index to 105.6 over the next three months.
The FTI index surveys 45 industry sectors, with 1,045 member businesses in the country. The index below 100 indicates declining confidence of the industry sector and above 100 demonstrates its better economic mood.