make sure a Pokemon in your party knows the move Rock Smash.
walk up to the rock you want to smash and press the "A" button
Chat with our AI personalities
You can break rocks by using the move Rock Smash.
You need to use the move Rock Smash which you get in Mauvile City.
get the HM strength, and teach it to a Pokemon
There is no TM that can Break rocks in Pokemon leaf green there is however in HM that breaks rocks called RockSmash
HM06 Rock Smash