Samples were collected from Gambia's Tanji Bird Reserve, around 20 kilometers from the capital Banjul, following reports of unusual deaths among wild birds.
The samples were sent to a laboratory in Dakar on April 1 and tested positive for High Pathogenicity Avian influenza (HPAI) type H5N1, said the statement, which was issued on Wednesday.
Authorities "are closely working together to help reduce the infection pressure at the wild bird level while working... to prevent the spill over to our poultry," it added.
Gambia is almost entirely surrounded by Senegal, which reported an outbreak of H5N1 bird flu on a poultry farm in the northwestern part of the West African country last Friday.
That outbreak occurred on March 18 on a farm in the village of Potou near the town of Louga, not far from the Langue de Barbarie National Park, where an outbreak of HPAI type H5N1 bird flu was found on March 10.
The same disease was first detected on March 8 in samples taken from migratory royal and sandwich tern birds around the Pink Lake, and Yoff Island near the capital Dakar, according to Senegalese authorities.
The outbreak on the poultry farm in Potou killed 500 birds, while the remaining animals in the 11,400-strong flock were culled. Over 1,700 wild bird deaths have also been recorded in Senegal.
Avian influenza, commonly called bird flu, has been spreading around the world in the past year, killing more than 200 million birds, sending egg prices rocketing and raising concern among governments about human transmission.