Abstract. – The cardinal fish Apogon imberbis (Linnaeus, 1758) is a common species in the Mediterranean sea but its reproductive biology is poorly known. Here we present information on the duration of the breeding season, the daily activity pattern and the mating behaviour of A. imberbis in the field, recorded in an Italian Marine Protected Area (Catania, Sicily). Mouthbrooding males were observed from July to September. Courtship behaviour was recorded throughout the day, however its highest frequency, as well as spawning, occurred at sunset. The abundance of cardinal fish varied during the study period, reaching a peak during the breeding season, when individuals exhibit site fidelity. Observations of mouthbrooding males and collection of egg masses allowed to estimate that parental cares last for 5 to 7 days, and brood size is around 4000-6000 eggs.