Mew’s National Pokédex number is 151.
Mew is a Mythical Pokémon associated with the first generation of the series. It appears after Mewtwo in the original National Pokédex numbering, making it the final entry in the original 151-Pokémon roster.
Mew was not normally obtainable through ordinary gameplay in the original Pokémon Red, Green, and Blue releases. It was distributed through special events and promotions, which helped create a long-running mystery around its existence and availability.
Mew is often confused with Mewtwo because their names and genetic story are connected. Mewtwo is number 150 and is described as a clone or genetic modification derived from Mew. Mew itself is number 151 and is classified as a Mythical Pokémon.