In order to establish a reasonable method to measure the endogenous phosphorus output in meat ducks, P-free method, regression analysis method and difference method were used to measure the endogenous phosphorus output in meat ducks. One hundred and fifty 21-day-old healthy male cherry valley ducks were randomly assigned into 5 treatments with 6 replicates per treatment and 5 ducks per replicate. P-free pure diet was formulated with P-free feedstuffs. Soybean meal was used as the only source of phosphorus to formulate 4 P-low gradient diets containing different levels of phosphorus (0.20%, 0.35%, 0.51% or 0.55%) based on corn starch. Titanium dioxide (TiO2) with the supplemental level of 0.4% was added to experimental diets as exogenous marker. During 21- to 24-day-old, all ducks were fed with complete pellet feed. During 25- to 30-day-old, ducks were fed with experimental diets and the feed intake recorded by replicate. The excreta were collected by replicate from 28- to 30-day-old. All samples were air-dried, and total phosphorus and TiO2 contents were measured. Endogenous phosphorus output was calculated. The results showed that there was no significant linear relationship between dietary phosphorus input and fecal phosphorus output (P<0.05), and the endogenous phosphorus output remained relatively stable. The endogenous phosphorus output in meat ducks was 1.20, 0.37 and 0.29 g/kg DMI, respectively, when measured by P-free method, regression analysis method and difference method. In conclusion, the endogenous phosphorus output in meat ducks can be measured by both regression analysis method and difference method, but a larger error was caused by P-free method.［Chinese Journal of Animal Nutrition，2011，23（3）：403 -409］