As in other regions, the Hoenn region holds a number of Gym located throughout the area. In all of the games and their remakes there are a total of eight Gyms. In the Pokémon Anime, the main character Ash, battled at eight Gyms as well. However, as seen with several characters' Badges, there were other unidentified Gyms that were not shown.
Rustboro City GymThe Rustboro Gym is located in Rustboro next to a large house (inside there is a boy willing to trade the main character a Seedot for a Ralts). The Rustboro Gym contains 3 trainers (who use rock and rock-ground type Pokémon). It is kind of like a maze but if manouevered properly, can dodge all three trainers. Here are some tips from the official guide: The Rustboro City Gym has a simple design. There are three Pokemon Trainers in the gym to warm up with. Both Trainers and Roxanne use Rock-and-Ground-type Rock-type Pokémon. Bring along any Pokémon that have Grass- or Water-type attacks to earn an easy victory. If you chose Torchic as your first Pokémon, the battle will be a little harder than if you'd chosen Treecko or Mudkip. Although Makuhita is a Fighting-type Pokémon(one can be found in Granite Cave), it is probably a good choice to take into the battle with you.
Dewford Town GymBrawley is Gym Leader, a master of Fighting-type Pokémon. The best Pokémon you could have here is Taillow or Swellow. Ralts/Kirlia is a good choice too, as is Zubat. When you enter his gym the first time, it is completeley dark, but as you progress, the range of vision will get bigger. And if you want to you can skip this gym until later in the game.
Mauville City GymThe Mauville gym has electric fences in it requiring you to step on tiles to shut them down and bring new ones up. The Gym Trainers use Electric-type Pokémon or Pokémon that know Electric-type moves like ThunderPunch. The Mauville gym leader Wattson, uses Electric-types and gives out the Dynamo Badge plus TM34 to those who can beat him.
Lavaridge Town Gym
The Lavaridge Town Gym has two levels: the ground floor and the b1 floor. Each floor has a series of holes that you can fall in or shoot up from depending which floor you're on. With proper backtracking you can get to the gym leader, Flannery.
Petalburg City Gym
This gym is consistent of nine rooms: The entrance room, the Gym Leader room and seven other rooms. Each room has a trainer who uses a different battle item depending on which room you choose.
Fortree City Gym
Mossdeep City GymIn Pokémon Ruby and Pokémon Saphire, the Mossdeep Gym consists of directional tiles with a few tiles that can change direction by a switch that is often guarded by a trainer. Here you had to face the twin Gym Leaders, Tate and Liza, in a double battle. All the trainers in this Gym use Psychic- type Pokémon so bring in any Dark- or Ghost- type Pokémon with you.
In Pokémon Emerald, it consists of warp panels , mutiple rooms,and cololred tiles that rotates a group of four directional tiles with the same color arrow as the tile that you stepped on. Most of the time, the colored tile when stepped on rotates multiple groups of directional tiles. All of the groups of directional tiles have at least one trainer or statue on it. In this version of the gym, all the trainers challenge you to double battles, including the Gym Leaders Tate and Liza.
This is the only Gym in the Hoenn reigon that had its format changed when the third game in that reigon came out.
Sootopolis City Gym
Sootopolis City Gym has two floors. The trainers are on the floor below and they are all female. In Ruby and Sapphire, Wallace is the Gym Leader, but in Emerald, Juan is the Gym Leader. The Gym's main floor is an ice puzzle where you have to step on each ice panel one. Stepping on a cracked ice panel again would result in falling to the trainers floor.