This study investigated Holothuria tubulosa, Gmelin 1791 in the Dardanelles Strait from April 2013 to March 2014, in order to outline the morphological characteristics, reproductive patterns and the relationship between population characteristics and environmental parameters. 15 to 30 individuals of this species were sampled monthly at three stations. There was a negative allometry between length and weight, with gutted weight being the most reliable measurement for this species. The reproductive patterns of the species were identiied for the irst time for examples from the Turkish coast. By macroscopic examination of the gonads, the smallest sizes ( gutted length) were measured as 8.4 and 8.1 cm for the female and male, respectively. The sex ratio ( female: male) was calculated as 1: 1.1 with differences between seasons. Reproduction of sea cucumbers occurred between August and September after Gonadosomatic Index ( GSI) values reached their maximum in July. The species was found at up to a 10 m depth with a population density of 0.21 / m(2), which was rather low compared to previously reported values for Mediterranean populations of this species. There was a high positive correlation between population density and GSI of the species. The highest population density was observed where the largest sea grass meadows are found.