More than a third of South Korea's listed companies experienced earnings surprises in the first quarter on the back of improved results among large firms, data showed Sunday.

A total of 31 out of 100 listed firms that filed earnings reports for the January-March period as of April 30 posted better-than-expected operating profits, according to the data compiled by market tracker FN Guide based on an assessment of 100 listed firms on the benchmark KOSPI and tech-laden KOSDAQ markets.