The Proteas play five one-day internationals and three Twenty20 matches between July 20 and August 6 in capital city Colombo, Kandy and Hambantota.
"We are resting Steyn as we have a very important and crowded Test season ahead," Cricket South Africa selection convener Andrew Hudson told reporters here.
"We want to be absolutely certain that Dale, as the leader of our attack, is properly rested and fit.
"Graeme Smith could not be considered because of his long-term recovery process following surgery."
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The tour marks the debut of new Proteas coach Russell Domingo and he will be in charge of 16-strong ODI and T20 squads with 12 cricketers included in both.
Hashim Amla, Colin Ingram, Alviro Petersen and Robin Peterson play only in the five-ODI series spread over 12 days at three venues.
Henry Davids, recalled Imran Tahir, Wayne Parnell and uncapped David Wiese were picked exclusively for three T20 games over five days.
"David impressed when the national emerging squad toured Namibia, having previously done well in the Champions League tournament," said Hudson.
Adrian Birrell has been named assistant coach to Domingo and Claude Henderson specialist spin bowling coach, and Allan Donald has been retained as specialist bowling coach.
Domingo was promoted after assisting former India World Cup-winning coach Gary Kirsten, who did not renew his two-year contract.