An electrophoretic examination of 21 presumptive loci was used to analyze the genetic relationship in the fish family Mullidae. The present study included seven species from the Red Sea and two from the Mediterranean. Two of the Red Sea species (Upeneus pori and U. moluccensis), which had colonized the Mediterranean via the Suez Canal, were also sampled in their new habitat. The electrophoretic results support the taxonomy which is based on morphomeristic measurements, with the exception of U. pori, the genetic distance of which with its congeneric species is at a level which is attributed to different genera. No discernible genetic difference was found between the populations of the colonizing species in both seas (D= 0.004 for U. moluccensis, D= 0.081 for U. pori), as well as between colonizing and non-colonizing species. The average heterozygosity of Mullidae is lower than the average known for other fishes.