Dewani announced this on the first day of his trial on Monday, four years after his wife was found shot dead in an abandoned car.
Dewani is accused of conspiring with a taxi driver to stage a car-jacking as the couple were driven through Gugulethu, a township on the outskirts of Cape Town, in November 2010.
He says they were kidnapped and his wife Anni abducted. The former model was later found several kilometres away in another township, dead from a single gunshot wound.
A tired looking Dewani, 34, dressed in a black suit and white shirt, appeared before Judge Jeanette Traverso at the Cape High Court packed with media and Anni's family, who wore ribbons and smiling pictures of her pinned on their jackets.
"I plead not guilty to all five counts, my lady," Dewani told the judge on the first day of his trial, after the state's prosecutor read out the charges including murder, kidnapping and robbery with aggravating circumstances.
If found guilty, he could spend up to 25 years in jail.
Dewani lost a three-year legal battle in Britain to avoid being tried in South Africa, where three men convicted in connection with the killing of his wife have implicated him in the crime, dubbed the "honeymoon murder."
It was the second high-profile trial this year to put South Africa's judicial system and high murder rate into the full spotlight of the world's media.
(READ MORE: Oscar found guilty on culpable homicide)
Olympic and Paralympic track star Oscar Pistorius was convicted of culpable homicide last month, escaping the more serious charge of murder for the killing of his girlfriend.