The lightning struck at three different places while rains lashed parts of the state.
Police officials said the first incident took place in Mechkurahi village in Faizabad district where lightning struck Maqbool Ahmad (50) and Ram Bali (25), while they were sitting in the courtyard of a house. Both were killed instantly.
The second incident took place at Mahayein village in Ambedkar Nagar district when a farmer, identified as Rajendra, was working in his field and lightning struck him and two other labourers. While Rajendra died on the spot, the other two were rushed to hospital with injuries.
The third incident took place at Rasoolpur village in Sultanpur district when lightning hit an orchard and killed two children - Abdullah (9) and Aslam (10).