Racist graffiti has been plastered over one of the walls at Cradley Heath Central Mosque and Islamic Centre on Plant Street.
The graffiti which was discovered yesterday, was daubed in white paint on the red brick wall made reference to the English Defence League.
This attack comes four years after the mosque was targeted by arsonists and burnt to the ground on Boxing Day in 2009.
The mosque was a thriving part of the community with 400 worshippers using it and classes of children being taught there. The worshippers had to find somewhere else to worship and the new mosque has now been targeted by the vandals.
Sandwell Council deputy leader Councillor Mahboob Hussain said: "We do not want to see graffiti like this anywhere in the borough. We have been made aware of this case and the slogan will be removed within four hours."
Supt Bas Javid said: "A police investigation has been launched following the discovery of offensive graffiti on Cradley Heath Mosque and Islamic Centre's wall. This comes after as police reveal they are looking for a second man in connection with the home-made bomb found near a Walsall mosque.