The net was installed at Fish Hoek beach, where Great White sharks are common and three attacks have taken place since 2004 - two of them fatal.
The small meshed net will act like an "underwater fence", said Gregg Oelofse, Cape Town's head of environmental policy and strategy.
It has been designed to avoid trapping sea life, unlike larger, more traditional meshed shark nets, he said.
The net will be trialled until January next year, to determine whether it works as a safety measure and if it will put marine life at risk.
"If we can be successful with an exclusion net, we can create a safe bathing space with no harm to the wildlife that comes into the bay," said Oelofse.
Fish Hoek beach has seen several violent shark attacks over the years.
The last fatality was in 2010, but a year later, a British man was badly mauled after ignoring warnings that sharks were in the area.
The net will be put up and removed daily to try and avoid whales and dolphins becoming entangled and trapped.