The Society of Motor Manufacturers and Traders said production dipped 1% last month against October last year, to 151,795 units.
However, exports rose for the 15th month in a row, with 122,765 cars built for overseas markets, a 1.7% rise.
This offset a 10.9% fall in production for the home market.
Exports accounted for 80.9% of UK production in October.
The SMMT said the UK motor industry remained strong, with production up by 9.2% so far this year, and more than 1.4 million vehicles produced.
SMMT chief executive Mike Hawes said: "October's figures underline the export-led nature of the industry, with eight out of 10 cars built for overseas customers.
"Despite model changes which have ended the consistent growth pattern of the past year or so, we are still on track for a record number of exports."
Concern about the UK car industry's position in a post-Brexit world has prompted executives to urge the government to help shield the sector from any deterioration in trade relations.
Government promises of "support and assurances" to Nissan helped persuade the Japanese carmaker to build both the new Qashqai and the X-Trail SUV at its Sunderland plant.
Mr Hawes said in a statement on Thursday: "Given this dependence on global trade, it is crucial that British-built cars remain attractive to international buyers and exports are not subject to additional tariffs, costs and other barriers to successful trade.
"It is also essential government ensures there is economic stability and a competitive business environment to ensure we continue to attract the global investment that is behind this performance."
UK car manufacturing slipped in October for the first time in 14 months amid slower domestic demand, according to the industry's trade body.