SMK Sultan Badlishah (Sultan Badlishah National Secondary School; abbreviated SMKSB) is a secondary school in Kulim, Kedah, Malaysia.

It is the third English-medium school to be established in Kedah and the first secondary school to be established in southern Kedah (catering the Kulim, Baling and Bandar Baharu districts).

The idea to establish the school was initiated and led by Syed Omar bin Syed Abdullah Shahabuddin, the then Kulim District Officer.

Prior to the school's establishment, parents have no choice but to send their children to secondary schools in Bukit Mertajam or Sungai Petani.

The school celebrated its Silver Jubilee in 1973 and its Golden Jubilee in 1998, officiated by the Kulim District Officer, Tuan Syed Harun Al Jafree and the Minister of Education, Dato' Sri Najib Razak respectively.