Confidence on political stability also plunged to the 76-month low, from 53.1 points in November to 46.6 points.
The index fell to 73.4 points in December from 75 points in the previous month.
"Political uncertainties tend to continue. This pressures the confidence. The index or consumption could recover early of the second quarter, at the earliest," Thanavath Phonvichai, director of UTCC's Centre for Economic and Business Forecasting.
He noted that the Thai economy would remain fragile in the first quarter and growth may be as low as 1-2 per cent as in the fourth quarter of last year.