The former physics professor at Dhaka University also said practising any religion is someone's personal matter.
"It's not a matter of even any group. It's my very personal decision to make which religion I will practice," he said at a programme in the capital on Friday.
"Bangladesh is going through various crises. According to the Constitution, Bangladesh is a secular democratic state. But we have established Islam as the state religion and kept it on the preface of the Constitution," the professor said.
The professor was speaking as the chief guest of the Ninth National Council of Bangladesh College University Teachers' Association.
He urged Prime Minister Sheikh Hasina to move forward to bring a bill in Parliament to strike off state religion from the Constitution in order to 'save' it and reinstate 'actual secularism in it'.
Prof Roy, who is also the Shikkha Andolan Mancha president, demanded implementation of the education policy, terming it 'democratic and secular to some extent'.
He slated the exclusion of secular writings in textbooks 'following Hifazat-e Islam demands'.
"How dare they removed works of Kaikobad, Abdul Wadud?" he asked.