After beating her unconscious and bringing her to his house, Kyung-chul methodically dismembers her, unaware of her ring dropping and getting stuck in the floor drain.

Soo-hyun drives to Kyung-chul's house, where he tortures him, places him under a makeshift guillotine and leaves him holding a rope between his teeth to keep the blade from falling.

Though he mocks Soo-hyun, Kyung-chul begins to panic when he learns that his son and elderly parents, whom he had abandoned some time ago, have arrived and are trying to visit him.

The Korea Media Rating Board forced Kim to recut the film for its theatrical release, objecting to its violent content.

The film received a "Restricted" rating twice, preventing any sort of release in theatres or on home video and promotions as well.

[12] The review-aggregation website Rotten Tomatoes gives the film a score of 81%, with an average of 7.2/10, based on 86 reviews from critics.

The website's consensus says: "Never flinching during its descent into depravity, I Saw The Devil is a pulverizing thriller that will give bloody satisfaction to audiences who like their revenge served with fiery rage.

[4] Jeannette Catsoulis of The New York Times wrote, "From an unexpectedly moving first act to a hilariously disgusting sojourn with Kyung-chul’s cannibal pal, Mr. Kim and his cinematographer, Lee Mo-gae, retain complete control of the film’s fluctuating tones and impressive set pieces.

"[14] Mark Olson of the Los Angeles Times wrote, "There is all the violent mayhem, for certain, but the thing that sets I Saw the Devil apart is its undercurrent of real emotion and how unrelentingly sad it can be.

"[16] Bloody Disgusting's Brad Miska gave it a rating of four-and-a-half out of five, writing: "I could talk for hours about I Saw the Devil, but nothing I can say will ever do it justice.

"[18] Phelim O'Neil from The Guardian wrote, "There's no shortage of Korean revenge-thrillers, but this, along with the recent The Man from Nowhere, proves there is plenty of life left in the genre" and gave it a four star rating out five.

[20] Elizabeth Kerr of The Hollywood Reporter wrote that, "On any number of levels, Devil is troublesome at best, offensive at worst.