Former prime minister Dr Mahathir Mohamad has expressed sadness after "returning" to Parliament, because of what is transpiring within its walls.

"I think I might have been here for some social events (after retirement in 2003), but this is the first time I am visiting the new building.

"It looks very (nice). It is a fantastic building, but I don't feel happy. I feel sad. The building is okay, but the content is not," Mahathir told reporters after attending an opposition meeting to discuss the erosion of parliamentary immunity.