Background and Objectives: Marine catfish are abundant in the bays of Tabounsou and Sangareah in Republic of Guinea, but the knowledge on their biology is still scanty. The reproductive biology of Arius latiscutatus Günther, 1864 and A. gigas Boulenger, 1911 was studied through monthly sampling, from January to December 2016. Methodology: Fish were caught using gill nets in several sampling sites. Five gonadal stages were described, based on macroscopic observation of gonad form, size, weight, color and oocyte diameter. Results: The population was dominated by males (61%) in A. latiscutatus and females (53%) in A. gigas, showing a sex-ratio of 1:1.54 (Chi-square, P < 0.05) and 1:0.88 (P > 0.05), respectively. The length-weight relationship was a positive allometry for A. latiscutatus and A. gigas, and males (35.37 and 35.47 cm, respectively) reached first maturity earlier than females (39.7 and 40.8 cm, respectively). Changes in the gonadosomatic index (GSI) and in stages of gonadal development showed that A. latiscutatus spawned between April and October, while A. gigas spawned in May to November. The peak of condition factor was observed in June (0.68±0.05) and July (0.55±0.04) in females of A. latiscutatus and A. gigas, respectively. Conclusion: Both species, having only one annual breeding season, A. latiscutatus spawns earlier than A. gigas. Coastal fisheries should be restricted in cold season to preserve the ability of broodstock renewal for these species.