Styris injured his back playing for Middlesex in the English county championship last month and was the most in doubt among a bowling line-up which has had to overcome a raft of injuries this year.
Styris pulled out of his last English county game on September 10, a week after the back pain first flared.
"I wasn't too sure when I came down to this camp how it would go but I've been bowling for five to six days at 100 percent intensity and haven't felt it at all," Styris told reporters Wednesday.
Team manager said Styris had been given the all-clear along with several other bowlers returning from injury.
Speedster Shane Bond, left arm spinner Daniel Vettori, all rounder Jacob Oram and pace bowler Kyle Mills are all returning from injuries which disrupted their careers during the past season.
Potential match winner Bond is coming back from a knee injury which forced himn home from New Zealand's three-test tour of South Africa in April and said he was back to full speed but lacked match fitness.
"I've prepared myself as well as I can again. My fitness levels are the same as they were two years ago. It'll just be nice to have a few overs under my belt," Bond said.
"I know I'm ready to go."
New Zealand, who won the trophy in 2000 when it was known as the ICC Knockout, open their campaign against South Africa on October 16.