Domestic passenger vehicle (PV) sales declined marginally to 2,38,692 units in December from 2,39,723 units in the same month previous year.
For 2018, PV sales rose 5.08 per cent to 33,94,756 units from 32,30,614 units in 2017.
Motorcycle sales last month, however, rose marginally to 7,93,061 units as against 7,88,334 units a year earlier.
Total two-wheeler sales in December declined 2.23 per cent to 12,59,026 units compared to 12,87,766 units in the year-ago month.
Sales of commercial vehicles were down 7.8 per cent to 75,984 units in December, SIAM said.
Vehicle sales across categories registered a decline of 2.97 per cent to 16,17,356 units from 16,66,878 units in December 2017, it added.