The Nissan Diesel Big Thumb (Japanese: 日産ディーゼル・ビッグサム) is a heavy-duty commercial vehicle that was produced by the Japanese manufacturer Nissan Diesel (now UD Trucks) and sold between 1990 and 2014, although Japanese sales ended in 2005, a few months after it had been replaced by the Nissan Diesel Quon.

[2] Unlike its predecessor, the Nissan Diesel C-series, the Big Thumb was primarily available as a full-size truck.

The Big Thumb's principal competitors were the Mitsubishi Fuso Super Great, Isuzu Giga and Hino Profia.

The Big Thumb has been succeeded by the Nissan Diesel Quon.

In Southeast Asia (Thailand, Malaysia, and Indonesia), a variant of this truck was sold as the Nissan Diesel Convoy/CWM series which uses Nissan Diesel Condor cabin but with mechanicals, engines, and drivelines from Nissan Diesel Big Thumb or Resona.