Ammonia (NH3 ) emission is a major concern for the poultry industry. The objective of this research was to determine whether inclusion of dietary fiber and a reduced dietary CP content would decrease NH3 emission from laying-hen manure. A total of 256 Hy-Line W-36 hens were fed diets with 2 levels of CP (normal and reduced) and 4 fiber treatments in a 2 × 4 factorial arrangement. The fiber treatments included a corn and soybean meal-based control diet and diets formulated with either 10.0% corn dried distillers grains with solubles (DDGS), 7.3% wheat middlings (WM), or 4.8% soybean hulls (SH) to contribute equal amounts of additional neutral detergent fiber. The CP contents of the reduced-CP diets were approximately 1 percentage unit lower than those of the normal-CP diets. All diets were formulated on the basis of digestible amino acid content and were formulated to be isoenergetic. Fresh manure was collected such that pH, uric acid, and Kjeldahl N contents could be measured. The NH3 emission from manure was measured over 7 d by placing pooled 24-h manure samples in NH3 emission vessels. Data were analyzed by ANOVA with Dunnett’s multiple-comparisons procedure to compare results from the fiber treatments with the control, whereas the main effect of protein was used to compare the normal- and reduced-CP treatments. Dietary corn DDGS, WM, or SH lowered (P ≤ 0.01) the 7-d cumulative manure NH3 emission from 3.9 g/kg of DM manure for the control to 1.9, 2.1, and 2.3 g/kg of DM manure, respectively, and lowered (P < 0.05) the daily NH3 emission rate. Results of this study showed that dietary inclusion of 10.0% corn DDGS, 7.3% WM, or 4.8% SH lowered NH3 emission from laying-hen manure; however, reducing the CP content by 1 percentage unit had no measurable effect on NH3 emission.