The Brushtooth Lizardfish Saurida undosquamis is one of the economically successful Lessepsian species, which migrated from the Red Sea to the Mediterranean Sea. The present study was carried out from September 2018 till April 2019 in the Northern Gulf of Suez (at Suez) and from March 2018 to March 2019 in the South-Eastern Mediterranean Sea (at Port Said). A total of 838 specimens were monthly collected from both sites. Overall sex ratio was 1:0.40 and 1:0.54 for the Gulf of Suez and the Mediterranean population, respectively. There was a highly significant difference between the ratios of both sexes in both populations (P<0.001). The monthly changes in maturity stages and gonado-somatic index showed that S. undosquamis have a prolonged spawning season extending from December to April in the Gulf of Suez and from June to March, with two major spawns occurring in August and February in the Mediterranean Sea. The fish length corresponding to 50% (L₅₀) was 17.3 cm for males and 18.2 cm for females from the Gulf of Suez, whereas it was 16.9 cm for males and 17.8 cm for females from the Mediterranean Sea. The absolute fecundity for the Gulf of Suez population ranged from 14750 to 63553 ova (average: 38075 ± 18181 ova) for fish that ranged from 20-22 cm to 30-32 cm (TL). For the Mediterranean Sea population, the absolute fecundity ranged from 18090 to 62025 ova (average: 39274 ± 15783 ova) for fish that ranged from 18-20 cm to 30-32 cm (TL).