The present invention relates to a read-only disk containing sample data and a reproducing method thereof. According to the present invention full data is encrypted and recorded on a read-only disk with additional non-encrypted sample data, which is a part of the full data, and navigation data used for searching for the sample data is also recorded on the read-only disk. And, when the encrypted data on the read-only disk is requested to be reproduced the sample data found with reference to the navigation data is reproduced instead if there is not an authenticated decryption key Owing to the present invention, a user can confirm easily whether a read-only, disk has encrypted contents he or she wants, which will lead to purchase of its decryption key as a natural result.