Balloting was done in 56 constituencies, including in Lucknow. As many as 967 candidates were in the fray in this round.
An election official died of a heart attack in a Lucknow polling booth, police said, but voting proceeded peacefully in all nine constituencies of the district, with young voters turning up in large numbers.
Voting began at 7 a.m. The morning chill initially kept many voters in the confines of their homes, but picked up as the day progressed.
Around 1.72 crore voters are eligible to elect their representatives spread across 11 districts -- Lucknow, Hardoi, Unnao, Rae Bareli , Chattrapati Shahuji Maharaj Nagar (Amethi), Farrukhabad, Kannauj, Banda, Chitrakoot, Fatehpur and Pratapgarh.
All parties claimed that the high number of voters would go in their favour.
Ruling Bahujan Samaj Party (BSP) chief and Chief Minister Mayawati, while casting her vote here, said: "My party will do even better than 2007."
Congress attributed the brisk polling to its youth icon Rahul Gandhi.
State Congress chief Rita Bahuguna Joshi said: "The higher voter turnout is attributable to the painstaking campaign carried out by Rahul Gandhiji and I have reason to believe that the youth of this state is impressed by him. Therefore, Congress is all set for a major stride and return to power in this state."
On the other hand, BJP leader Uma Bharti said, "BJP is all set to get a majority in the state."
Asked how the former Madhya Pradesh chief minister became a voter in Uttar Pradesh, she said, "Since I have been working here for some time, I decided to get my vote shifted from Tikamgarh in Madhya Pradesh to this city."
Senior BJP leader Rajnath Singh told reporters: "First of all I must thank the Election Commission whose efforts are responsible for this appreciable rise in the voter turnout today.
"But another important fact that cannot be ignored is that voters are coming out in larger numbers, simply to express their anger against the misdeeds of the ruling BSP as well as SP, whose misgovernance they have experienced just prior to Mayawati's rule."
As many as 18,000 polling stations were set up across the state.
This phase has as 103 candidates with criminal cases pending against them.
About 139 multi-millionaires ('crorepatis') are also in the fray in the fourth phase that would test the fate of several political heavyweights, including three ministers, 32 sitting legislators and 12 former ministers.
This round will be an acid test for the ruling BSP which had the maximum at stake, since the party had bagged 25 of these 56 seats in 2007.
Samajwadi Party was also not far too behind with a tally of 14, while the Bharatiya Janata Party (BJP) and Congress had bagged seven seats each in the last assembly election. Two seats had gone to independents, while two new constituencies came up on account of delimitation of seats.
The fourth phase of the Uttar Pradesh state assembly election also draws significance from the fact the three of India's prime ministers were elected from here. These include Rajiv Gandhi, who repeatedly romped home from Amethi, Vishwanath Pratap Singh, who was elected from Fatehpur and Atal Bihari Vajpayee, who made Lucknow his political abode.
The last round of the seven-phased election to the 403 member assembly in India's most populous and politically crucial state will be held on March 3 and votes will be counted on March 6.