The UN chief’s concern is contained in the UN official statement made available to newsmen in New York.
Ban said the UN was against the use of the death penalty in all circumstances.
The secretary-general urged the Egyptian government to ratify the second optional protocol of the International Covenant on Civil and Political Rights and to impose a moratorium on the death penalty.
The UN boss also said he was concerned that such verdicts, handed down after mass trials, might have negative impact on prospects for long-term stability in Egypt.
He, therefore, underscored the importance of pluralism which included the guarantee that all voices were heard and represented in the matter.
He, however, pointed out that the sentences were subject to appeals, adding that the authorities must ensure the defendants benefitted from due process and fair trial.
Tuesday would qualify as a day of multiple judgment for the former Egyptian leader.
A court had earlier sentenced him to life imprisonment for conspiring with foreign groups.
Same day, he was sentenced to death on charges of killing, kidnapping and other offences during a 2011 mass jail break.
The general guide of the Muslim Brotherhood, Mohamed Badie, and four other Brotherhood leaders were also handed the death penalty. More than 80 others were sentenced to death in absentia.
Morsi became Egypt’s first democratically elected president after the downfall of longtime autocrat Hosni Mubarak in 2011 but was himself overthrown by the army in 2013 after mass protests against his rule.
The court last month convicted Morsi and his fellow defendants of killing and kidnapping policemen, attacking police facilities and breaking out of jail during the 2011 uprising against Mubarak.
The death sentence request had drawn criticism from the United States, other Western governments and human rights groups.
After Tuesday’s sentencing, a senior Muslim Brotherhood member said the trial had “fallen below all international standards”.
“This verdict is a nail in the coffin of democracy in Egypt,” Yahya Hamid, a former minister in Morsi’s cabinet and head of international relations for the Brotherhood, told a news conference in Istanbul.