The 2021 K3 League was the second season of the K3 League as a semi-professional league. The 15 participating teams played each other twice, and the bottom team was relegated to the K4 League.
Relegated to K4 League
Promoted from K4 League
Withdrawn
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When the first round and semi-final matches were finished as draws, their winners were decided on the regular season rankings without extra time and the penalty shoot-out.
Gimpo FC won 3âÂÂ2 on aggregate.