Shops did a brisk trade selling plastic roses and heart-shaped balloons, something that under their former jihadist rulers would have been a crime punishable by death.
Student Rafal Fathi donned a full-length black abaya and headed to a market in Muthana district to buy a red teddy bear.
"When I get home, I'm going to dress differently for the occasion," said the 22-year-old.
Asked who the gift was for, she blushed and refused to say.
But, she said: "I really want to send a message to the world that Mosul has changed."
The Islamic State group imposed a hardline interpretation of Islamic law on the city, seeing the feast of love as an abomination. Celebrating it was punishable by death.
Fathi said she was sure most people in Mosul would mark the festival this year.
Residents braved wintery rain to head to markets in the city's east, filled with red bears, roses and heart-shaped balloons.
"There's strong demand for Valentine's Day gifts that we make ourselves here," said 42-year-old shopkeeper Ahmad Seif al-Din.
"When Daesh arrived, we kept selling roses, but hidden in black bags," he said, using an Arabic acronym for the group.
"Then we stopped when they announced that celebrating Valentine's Day would be punishable by death."
East and west Mosul 'like lovers'
Today, the site of some of the jihadists' worst atrocities is packed with stalls selling Valentine's Day gifts.
The Prophet Younes market even hosted a group of young men dancing to the sound of an orchestra.
"Yesterday the market was where Daesh executed its victims, now it's a market of joy," said Mohammad Maan Zakaria, a civil society activist.
"This is the first time we've celebrated. The city needs joy and happiness," the 28-year-old said.
Much of the city, which is divided by the River Tigris, lies in ruins after years of IS rule and a months-long battle to oust the group.
While life has resumed on the east bank, the west lies comatose, covered with mounds of pulverised rubble.
Last year, the Azzuhur school in the city's east hosted a Valentine's Day party complete with plastic roses, balloons and multi-coloured confetti -- even as fighting raged in the west, at that point still under IS control.
Today, many are reluctant to celebrate openly, out of respect for the thousands of families who lost members, executed by the jihadists or killed as Iraqi forces backed by international coalition aircraft battled for the city.
"The massive destruction of infrastructure in Nineveh province (surrounding Mosul) and the murder of thousands of people means some people don't celebrate Valentine's Day in public," said 28-year-old unemployed Hisham Hamdun.
But Seif al-Din disagreed.
"Everyone should buy a red rose to fight the evil ideas of Daesh," he said.
People should place them "in front of a house or a store on the west bank, because like lovers, the two banks can't live separated from each other", he said.
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