<jats:p>Biological sampling of whitesnout guitarfish <jats:italic>Rhinobatos leucorhynchus</jats:italic>, caught as by‐catch in the commercial fisheries on the Pacific coast of Ecuador, was conducted from specimens caught between April 2013 and January 2015, in order to provide further information on the reproductive biology of this species, for which data are limited. Samples comprised 1024 specimens (458 males and 566 females), with the sex ratio (1:1·23) significantly in favour of females. The total length (<jats:italic>L</jats:italic><jats:sub>T</jats:sub>) ranged from 20·5 to 106·0 cm and showed sexual dimorphism, with females attaining a larger size. The relationship between body mass (<jats:italic>M</jats:italic><jats:sub>T</jats:sub>) and <jats:italic>L</jats:italic><jats:sub>T</jats:sub> was not significantly different between sexes. The length at 50% maturity for males based on internal reproductive organs was 60·9 cm <jats:italic>L</jats:italic><jats:sub>T</jats:sub>, which was slightly larger than when based on clasper condition alone (58·5 cm <jats:italic>L</jats:italic><jats:sub>T</jats:sub>). The <jats:italic>L</jats:italic><jats:sub>T</jats:sub> at 50% maturity for females was 57·8 cm, and the <jats:italic>L</jats:italic><jats:sub>T</jats:sub> at maternity was 65·1 cm. Fecundity ranged from one to seven embryos and <jats:italic>L</jats:italic><jats:sub>T</jats:sub> at birth was 20–26 cm<jats:sub>.</jats:sub> According to oocyte development, two peaks of ovulation were observed (May to June and November to December). The ovarian cycle was estimated at 6 months and gestation between 5 and 6 months. Embryos showed different sizes all year‐round, indicating an asynchronous cycle.</jats:p>