The bomber targeted the Muharram procession while it was being taken out in Jacobabad.
District police chief Shah Zaman Khuro confirmed the attack.
"So far 15 people have been killed and about 36 injured," he said.
Deputy Superintendent Police (DSP) Khuda Bakhash said it was a suicide bombing.
Police said that the death toll may rise as some of the injured were in critical condition.
The minority Shia's are regularly attacked by extremist Sunni militant groups in Pakistan who consider them as heretics.