The aim of this study  is to investigate the by catch from the Egyptian Mediterranean trawlers off Alexandria during the period from March 2018 and May 2019. The catch per unit effort (CPU) ranged from 4 Kg / hr in autumn to 9 Kg / hr in summer. Invasive species reached 44 in number; 43 species of Red Sea origin and one species of Atlantic Ocean origin.  The by catch was represented by one elasmobranch, 80 boney fishes and 14 invertebrates belonging to 4 phyla; 5 classes; 22 orders and 56 families. Eight families of fish were dominated and constituted the high rank of percentage during the period of investigation. 12 species were prevailing the by catch and constituted the high percentages namely: Spicara smaris (22.575%); Boops boops (12.922 %); Nemipterus randalli (8.943 %); Spicara maena (4.865 %); Synchiropus sechellensis (4.864 %); Diplodus vulgaris (4.504 %); Lepidotrigla cavillone (3. 313 %); Upeneus pori (3.225 %); Pagellus erythrinus (3.192 %); Mullus barbatus (1.804 %); Terapon puta (1.235 %) and Ariosoma balearicum (1.038 %).  Nine species occurred during the four seasons; 18 species were represented during three seasons; 17 species occurred in two seasons, while forty-nine species were represented in one season. The biological studies on the most economical by-catch species showed there were three species belonged to one year of life, eight species had two years of life and one species was found belonging to age group three.