Saddam was hanged for the killings of Shias following a 1982 attempt to assassinate him in the town of Dujail.
"Each year on this day, I remember the vicious attack carried out by Saddam against the peaceful city," Tuba Abid, who lost 22 relatives in the attack, said as she laid roses on a victim's monument in Halabja.
"The execution of Saddam has reduced my pains and I feel more secure after the death of this dictator."
Nuri al-Maliki, the Iraqi prime minister, had planned to attend the ceremony, but his aircraft was unable to land at the airport and was forced to return to Baghdad because of the bad weather, Kurdish officials said.
Moments of silence were held in Halabja, Dahuk, Irbil and Sulaimaniyah.
Othman Abdullah, 26, lost his brother during the attack, and said his father died last year from kidney failure and his mother of respiratory problems after years of illness stemming from the chemical agents.
"I watched the slow painful deaths of my father and mother and wondered when their suffering would end. I could not afford to send them outside Iraq so that they could receive the proper medical treatment," he said.
"After losing my brother, mother and father, life has become meaningless to me."
Abdullah criticised autonomous Kurdistan's regional government of doing little to help the victims of the chemical attack.
"The officials have done nothing to heal my father and mother, but the government is ready to send the children of the officials abroad if they receive the slightest injury," he said.