ABSTRACT. – Chaetophiloscia elongata Dollfus, 1884, an Holo-Mediterranean terrestrial isopod, is found in the Mediterranean regions but also on the coasts of the Black Sea. Its biology, population dynamics and life cycle were studied by monthly surveys performed from January 2010 to June 2011 at the banks of Menzel Jmil lagoon. The ovigerous females were present from February to November, suggesting that Chaetophiloscia elongata has a seasonal reproduction pattern. Female size was positively correlated with fecundity (number of eggs per brood) and fertility (numbers of embryos hatched per brood). Sex ratio was globally in favor of females (0.42). Analysis of the size frequency polymodal distribution showed that six cohorts were identified in the first sampling month and eleven new cohorts were detected during the next months. The length of newly born cohorts ranged from 1.32 to 1.78 mm. Lifespan was estimated at 8 to 10 months.