This study was conducted to investigate the effects of dietary calcium (Ca) concentrations on growth performance, litter quality, and tibia characteristics in growing broiler chickens. A total of 1,800 21-d-old broiler chickens were used and housed in floor pens for 2 weeks. Birds were randomly allotted to 1 of 6 dietary treatments with 6 replicates. Each replicate consisted of 50 chickens. Dietary Ca concentrations were set to 0.9, 0.8, 0.7, 0.6, 0.5, and 0.4%. Non-phytate P (NPP) was maintained at 0.3% and 0.02% of a 5,000 FTU/g phytase (Phyzyme XP, Danisco Animal Nutrition, Marlborough, UK) in all diets. After 2 weeks, 2 birds from each replicate were euthanized and tibia samples were collected. Litter samples were also collected from each pen floor. Pre-planned orthogonal polynomial contrast test was performed to determine linear and quadratic effects of dietary Ca concentrations. Results indicated that growth performance including BWG, feed intake (FI), and feed efficiency (FE) was not affected by dietary Ca concentrations. Litter quality including litter pH, litter moisture, and litter nitrogen was not influenced by dietary Ca concentrations. However, decreasing concentrations of Ca in diets from 0.9 to 0.4% decreased (linear and quadratic, P < 0.01) the concentrations of Ca and P in tibia. In conclusion, decreasing concentrations of Ca from 0.9 to 0.4% in diets containing 0.3% NPP and phytase (1,000 FTU/kg) decrease the concentrations of Ca and P in tibia, but no adverse effects on growth performance and litter quality in growing broiler chickens.