Pollimyrus isidori is an uncommon species of mormyrid fishes in the River Nile. The population caught, from the Nile Delta in the present study, was completely females. Five meristic and 23 morphometric characters of Pollimyrus isidori were   described; some of these measurements were significantly correlated with fish standard length (P > 0.05). Female has a single triangular-shaped left ovary in the dorsal side of abdominal cavity, just beneath the air bladder and attached to thecoelom by a thin short mesovarium. The spawning season extended from April to August; the period characterized by the highest values of ovarian-somatic index (4.3- 11.5 %) and ovarian weight (0.18- 1.07 g). The univariate and multivariate regression analyses of ovarian-somatic index versus water temperature; daily photoperiod and liver-somatic index, revealed highly significant correlation, suggesting that, the reproductive activities of Pollimyrus isidori are affected by the environmental conditions, and the liver serves the reproductive functions and structural proliferation of the ovary. The absolute fecundity ranged between 384 egg in April to 929 egg in July, and the egg diameters ranged between 1.33 to 1.92 mm and between 0.56 to 0.79 mm for the first and second generations, respectively. Females attain the first sexual maturity at an average 6.3 cm standard length. Pollimyrus isidori is an omnivorous feeder, its diet is composed of insects; plant fragments; algae; diatoms; crustaceans; annelids; detritus; unidentified eggs and sand. The population of Pollimyrits isidori feeds throughout the year, and this may explain the insignificant correlation (P> 0.05) of either stomach weight or stomach index with either water temperature or daily photoperiod or both of them.