The third generation (generation III) of the Pokémon franchise features 135 fictional species of creatures introduced to the core video game series in the 2002 Game Boy Advance games Pokémon Ruby and Sapphire. These games were accompanied by the television series Pokémon Advanced, which aired from November 21, 2002, until August 28, 2003, in Japan.

The following list details the 135 Pokémon of generation III in order of their National Pokédex number. The first Pokémon, Treecko, is number 252 and the last, Deoxys, is number 386. Alternate forms that result in type changes are included for convenience. Mega Evolutions and regional forms are included on the pages for the generation in which they were introduced.

Nintendo Life noted in a retrospective that the third generation of Pokémon has a very different "feel" from the two generations that came before it because almost all of its 135 new Pokémon – save for Azurill and Wynaut – have no relation to those of the previous generations. Ruby and Sapphire features two "Mythical Pokémon" – Jirachi and Deoxys – both of which became available to coincide with their respective anime movies.^[1]

Pokémon Ruby and Sapphire significantly increased the amount of "Dark" and "Steel"-type Pokémon in the series, as only a few Pokémon in previous generations used these typings. Hardcore Gamer also noted that many of the new Pokémon made use of "dual typing", where Pokémon have both a primary and a secondary type. This was not nearly as common in Red and Blue or Gold and Silver.^[2]

Reception to generation III's Pokémon has been polarized. Alex Carlson of Hardcore Gamer wrote in 2014 that the third generation of Pokémon games was not well received by fans of the series, with some people calling the generation the "worst in the series history".^[2] This was in part because Ruby and Sapphire did not allow players to transfer in their Pokémon from previous generations and, because of this, many older Pokémon were completely unavailable in the games until Pokémon FireRed and LeafGreen were released a few years later.^[66] Meanwhile, many of the new Pokémon designs, such as those for Torchic, Feebas, Luvdisc, Castform and Clamperl, were criticized for being unoriginal.^[2][66][67] Contrastingly, some designs, including Breloom, Aggron, and the aforementioned Castform were praised for their coolness, with the large variety of unique legendary Pokémon also helping the third generation feel fresh and new.^[68] While Ruby and Sapphire were recognized for introducing less memorable designs than their predecessors, designs like Milotic, Salamence, Metagross, Rayquaza, and Blaziken made the overall generation a satisfying supplement to the existing Pokédex.^[69]

The third generation has had its share of enduringly popular designs. Eighteen years after the release of Ruby and Sapphire, Rayquaza and Gardevoir finished eighth and ninth in 2020's Pokémon of the Year vote,^[70] with Flygon, Sceptile, and Blaziken also among the top 30.^[71] Rayquaza also finished eighth in a 2016 Japanese poll, with Jirachi and Kyogre among the top 25.^[72] A popularity vote on the Pokémon subreddit featured Blaziken at 5th, joined in the top 25 by Gardevoir, Absol, Flygon, and Mudkip.^[73]