The aim of this paper is to present an analytical study of gonad index (GI) and repletion index (RI) of Holothuria (Holothuria) tubulosa Gmelin, 1791 (Echinodermata Holothuroidea Holothuriidae). The study is based on biomonitoring data collected from February 2014 to January 2015 in the Oran coast. The gonad index of Holothuria tubulosa is analyzed to show the reproductive cycle and its relationship to environmental parameter conditions. Samples of 15 to 20 individuals were collected monthly at three stations on the Oran coast (La Madrague, Cap Carbon, and Ain Franin). The sex ratio of all sampling was found as (female: male) 0.8:1.2 with no significant difference between sites (X 2 = 2.18 ; df=4 ; p>0.05) and is also not significant regarding the seasons (spring, summer, autumn, winter) (X2= 3.03 ; df=6 ; p>0.05). Sea cucumber reproduction occurred in September at Cap Carbon and Ain Franin with values of Gonad index (GI) that are 0.33± 0.52 % and 0.22± 0.52 % respectively. At the La Madrague site, the spawning occurred in October with a value of GI of 1.49±2.03 %. It was observed that seawater temperature has a positive correlation with Gonad index (GI) and no correlation with Repletion index (RI).