Election officials said the percentage of turnout was provisional at the close of polling.
Rival sides have expressed confidence that the heavy turnout would see the outcome in their favour.
During the 2011 assembly elections, the polling percentage in the constituency was 70.61.
The bypoll was necessitated following the death of former Speaker G Karthikeyan who represented the segment (previously known as Aryanad) in the state assembly from 1991-2015.
In a three-cornered contest, UDF candidate K S Sabarinath, younger son of Karthikeyan, is taking on former Speaker and ex-minister M Vijaykumar (LDF) and former union minister, O Rajagopal fielded by BJP.
Film stars and television actors, including Kushboo, Suresh Gopi and Innocent, MP, had hit the campaign trail.
The bypoll is a litmus test for both the Fronts as panchayat polls are to be held later this year and assembly elections are just a year away.
During the campaign, while UDF spoke of development projects it had initiated, LDF attacked the ruling Front with various corruption allegations, including solar and bar bribery scams.
The assembly segment has a total electorate of 1,85,216 voters, with women outnumbering men.
The counting of votes will be held on June 30.
