The companies' combined US sales stood at 147,613 units last month, up 17.4 per cent from a year earlier, marking the highest combined sales for any previous October.
Hyundai Motor, including Genesis models, sold 78,705 units, up 18.3 percent, while Kia sales gained 16.5 percent to 68,908 units, reports Yonhap news agency.
The companies' eco-friendly vehicle sales surged 52 percent on-year to 31,668 units. Hybrid vehicles led the segment with an impressive 64.9 percent jump to 21,679 units, setting a new monthly record.
Hybrid versions of Hyundai's Tucson SUV and Kia's Carnival minivan, in particular, achieved strong sales growth last month, with the Tucson hybrid logging a 110 percent sales increase to 6,790 units and the Carnival hybrid model selling 1,941 units.
Meanwhile, Kia said on Monday it has released a revamped version of its K5 midsize sedan with an improved value proposition and a suite of feature upgrades.
The latest K5 features expanded safety and convenience options across its trims, with Kia adding a new entry-level trim called Smart Selection to the 2-litre gasoline engine model, offering a more affordable price point.
Kia has also standardised features, such as LED lighting on the sun visor and glove box, rear-seat floor mat hooks and an in-car fire extinguisher on all trims.
Starting from the Prestige trim, previously optional features like steering wheel vibration alerts and steering wheel heating are now standard.
A Kia official stated, "This year's updated model has significantly enhanced safety and convenience features, incorporating extensive customer feedback on the previous year's product improvement model to further elevate its competitive edge."