The vans, which were parked in Driver Street and Furnace Lane, Woodhouse Mill, each had tools worth over Â£1,500 stored inside.
South Yorkshire Police said vans have become a 'major target' for thieves in the city.
A spokesman said: "If you have a works van or know someone that does please make sure you or they empty it every night as they are a major target."
Anyone with information should call South Yorkshire Police on 101.
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