Two experiments were conducted to determine if supplementing broiler diets with defatted green microalgae (Nannochloropsis oceanica, 0.69% phosphorus, Cellana, Kailua-Kona, HI) affected bone properties and phosphorous nutrition. Data were analyzed using one-way ANOVA and(or) linear regression procedure (SAS Version 9.1, SAS Institute, Inc., Cary, NC). In Experiment 1, day-old male Ross broiler chicks (total = 180) were fed a corn-soybean meal basal diet (BD) containing 0 (Control), 2, 4, 8, or 16% of the defatted microalgae for 6 wk. Chicks were housed in cages (6/cage) and each treatment consisted of 6 cages. Supplemental microalgae had no effect on tibial maximum load, maximum slope, extension at maximum load, energy to maximum load, or weight. However, tibial length of birds fed the 16% microalgae diet was 6.9% shorter (113 ± 0.3 mm vs. 105 ± 4.6 mm, P < 0.05) than that of those fed the control diet. This decrease was consistent with a 10.2% lower BW of birds fed the 16% microalgae compared with the control (2817 ± 70.6 vs. 2528 ± 75.8 g, P < 0.01). There were dose-dependent increases (P < 0.01) in soluble inorganic phosphorous retention, and decreases (P < 0.05) in soluble inorganic phosphorous excretion with elevated microalgal inclusions. Plasma inorganic phosphorous concentrations were not affected by the diet treatments. In Experiment 2, 3-wk old male Cobb chicks (total = 120) were fed the control, BD + 10% microalgae, BD +10% microalgae + high vitamin E (DL-α-tocopheryl acetate, 150 IU/kg), or BD + 10% microalgae + high selenium (selenium-enriched yeast, 0.5 mg Se/kg) for 3 wk. Chicks were housed in cages (5/cage) and each diet treatment consisted of 6 cages. Compared with the control (BD), the other 3 diets produced no differences in all the tibial measures (including length) as described in Experiment 1. In conclusion, feeding broiler chicks with the defatted green microalgal biomass up to 10% in their diets did not show any adverse effect on bone health, but seemed to improve dietary phosphorus retention. Supported in part by a USDA/DOE Biomass R&D Initiative Grant, a Hatch Grant of Cornell University, and a Morley Student Research Fund Award of Cornell University.