Both models were awarded the Life Cycle Assessment (LCA) certificate from Germany-based TUV Nord for their environmental friendliness this week.
They join two other Kia cars, the Sportage SUV and cee’d family hatchback, in receiving the certificate.
The Kia Soul’s CO2 emissions are as low as 137g/km and the Venga emits just 117g/km from its best-performing model, the 1.4-litre diesel EcoDynamics model.
This translates to VED charges of £110 and zero for the first year, and the Venga rises to just £30 in the second year under the current road tax rates.
LCA results show, once developing, manufacturing and disposing of the cars is taken into account, the Soul and Venga emits 9.3 per cent and 10.5 per cent less CO2 than similar size models over a driving distance of 150,000km.
This is because Kia has investigated methods of recycling materials, making the dismantling process more efficient and shortening the manufacturing process by simplifying parts.
The Kia Soul is built in Korea, and the Gwangju Plant has already been awarded environmental certification in 2003. It was followed by the Slovakia Plant, where the Venga is built, in 2009.
The Kia Venga, a mini-MPV designed to give more space than a conventional supermini, is priced from £10,995 for a basic entry-level model, but the 1.4-litre CRDi EcoDynamics range starts at £12,260.
In comparison, the Soul compact SUV-style crossover starts from £11,350 on-the-road, but there is no EcoDynamics currently available in the range.