The cash-strapped team, who changed ownership in July and are fighting for their future, said the 32-year-old had been brought in to provide more feedback to improve the car's performance.
"The team will benefit from having another experienced driver at the wheel of the car throughout the weekend," Caterham said in a statement.
"The German's feedback will contribute to improve the performance of the car. The weather also plays a big role at Spa-Francorchamps and Lotterer is one of the most experienced drivers racing under mixed conditions."
Caterham said Kobayashi, who has driven for three Formula One teams and finished third in his home Japanese Grand Prix for Sauber in 2012, remained part of the team.
However, the popular Japanese brings little in the way of funding to the team and knew his place was insecure after previous owner Tony Fernandes, the Malaysian aviation entrepreneur, sold the team in July.
Lotterer is also a world endurance co-champion with plenty of experience of the Spa circuit.
While he has never raced in Formula One, the German - who grew up in Belgium - was Jaguar's Formula One test driver in 2002.
"I am delighted to be given the opportunity to take part in a Formula One race weekend," he said. "I'm ready for this challenge and I cannot wait to jump in the car and make the most out of the weekend ahead.
"I will need to get settled and used to the car quickly, as the team has worked on a number of updates and we will need to have as much time as possible out on track to optimise the car's performance."
Caterham's other driver is Swedish rookie Marcus Ericsson.
The British-based team have never scored a point in four and a half years of trying. They are currently 11th and last in the standings.
The new management, with former F1 team boss Colin Kolles as an advisor and key figure, has made scoring a point and finishing 10th overall the key target for the rest of the season.
Lotterer has previously raced for Kolles at Le Mans.
(Reporting by Alan Baldwin, editing by Ken Ferris)
