The study was carried out to determine the effect of density on Muscovy duck behaviour and reproductive performance. Duck reared in an outdoor pen , were monitored during the last part of their egg-laying period. The experimental period lasted 9 weeks and the animals were submitted to the following densities: 1st through 2nd wk: 1 bird/m2 (D1); 3rd wk: 2 birds/m2 (D2); 4th wk :D1; 5th wk:6birds/m2 (D6); 6th wk:D1; 7th wk:4 birds/m2 (D4); 8th through 9th wk:D1. The following parameters were recorded: egg production, individual live weight (LW), serum cortisol level and behavioural activities. Data suggest a reduction in well-being for animals reared in D6 and D4. The data indicate that the increased density is responsible for behavioural and haematological abnormalities suggesting a stressfull situation. However, this condition is reversible with the decrease in density and is not associated with a decrease in egg production.