He expressed his concern while winding up the debate in the upper house to commemorate the International Day of Democracy.
He said that constitutional check is needed to stop yet another military takeover in the country.
"I believe that Article 6 has become redundant. Our weaknesses have made it redundant. In my eyes, no constitutional clause can protect democracy," Rabbani said.
Civilian government in Pakistan has been toppled four times to directly rule the country and the military interventions continued despite Article 6 of the 1973 constitution which criminalises the abrogation of the constitution by declaring it as "high treason", which is punishable with death.
Pervez Musharraf was the last military ruler of Pakistan who took over in 1999 but was forced to resign in 2008.