2003 Arizona Diamondbacks season

The 2003 Arizona Diamondbacks looked to improve on their 98–64 record from 2002. They looked to contend in what was once again a strong National League West. They finished the season with a record of 84–78, good enough for third place in the division.

Offseason

 * December 15, 2002: Erubiel Durazo was traded by the Diamondbacks to the Oakland Athletics as part of a 4-team trade. The Cincinnati Reds sent Elmer Dessens and cash to the Diamondbacks. The Toronto Blue Jays sent Felipe López to the Reds. The Athletics sent a player to be named later to the Blue Jays. The Athletics completed the deal by sending Jason Arnold (minors) to the Blue Jays on December 16.
 * January 30, 2003: Ricky Bottalico was signed as a free agent by the Diamondbacks.
 * February 14, 2003: Scott Service was signed as a free agent by the Diamondbacks.

Regular season

 * September 19, 2003: Diamondbacks pitcher Randy Johnson hit a home run off of Milwaukee Brewers pitcher Doug Davis, his only home run in his MLB career.

Notable transactions

 * June 3, 2003: 2003 Major League Baseball draft
 * Conor Jackson was drafted by the Diamondbacks in the 1st round (19th pick). Player signed June 16, 2003.
 * Carlos Quentin was drafted by the Diamondbacks in the 1st round (29th pick). Player signed July 2, 2003.
 * June 16, 2003: Scott Service was selected off waivers from the Diamondbacks by the Toronto Blue Jays.
 * June 29, 2003: Matt Williams was released by the Diamondbacks.
 * July 29, 2003: David Dellucci, Bret Prinz, and John Prowl (minors) were traded by the Diamondbacks to the New York Yankees for Raúl Mondesí and cash.

Starters by position
''Note: Pos = Position; G = Games played; AB = At bats; H = Hits; Avg. = Batting average; HR = Home runs; RBI = Runs batted in''

Other batters
''Note: G = Games played; AB = At bats; H = Hits; Avg. = Batting average; HR = Home runs; RBI = Runs batted in''

Starting pitchers
Note: G = Games pitched; IP = Innings pitched; W = Wins; L = Losses; ERA = Earned run average; SO = Strikeouts

Other pitchers
Note: G = Games pitched; IP = Innings pitched; W = Wins; L = Losses; ERA = Earned run average; SO = Strikeouts

Relief pitchers
Note: G = Games pitched; W = Wins; L = Losses; SV = Saves; ERA = Earned run average; SO = Strikeouts