Sifat, 18, who was undergoing treatment at ICU, breathed his last in the morning, said Bacchu Miah, inspector of Dhaka Medical College Hospital (DMCH) police outpost.
Earlier on Saturday, two more blast victims died at the hospital.
Around 40 people were injured in the blast at a mosque in Fatullah after Esha prayer on September 4.
Of them, 37 were taken to the Dhaka hospital in critical condition.
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