To study the possibility of producing Muscovy duck (MD) * Game Farm Mallard (GFM) crosses in natural mating, the authors monitored the egg fertility (EF) of MD, GFM and their crossbreeding for one year. A total of 354 sexually mature birds were reared in outdoors pens and kept under natural light. The eggs were collected daily and incubated after a max storage of 7 days (d) (T=11°C, R.H. = 70%). The EF was determined by candling on the 10th d. The results showed that the Ef of MD and GFM differred (90.6% and 97.6% respectively, P<0.01) and the EF of their crosses is lower than purebreeds. All the experimental groups with the exception of GFM, reach their pick EF in the 2nd deposition month.