The objective of this experiment was to investigate the effects of dietary calcium (Ca) concentrations on growth performance, litter quality, and tibia characteristics in starter broiler chickens. A total of 2,520 one-day-old broiler chicks were used and housed in floor pens for 3 weeks. Birds were randomly allotted to 1 of 6 dietary treatments with 6 replicates. Each replicate consisted of 70 chicks. Dietary Ca concentrations were set to 1.0, 0.9, 0.8, 0.7, 0.6, and 0.5%. Non-phytate P (NPP) was maintained at 0.35% and 0.02% of a 5,000 FTU/g phytase (Phyzyme XP, Danisco Animal Nutrition, Marlborough, UK) was included in all diets. At the end of experiment, 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 Ca concentrations. Results indicated that decreasing concentrations of Ca in diets from 1.0 to 0.5% increased (linear, P < 0.05) BW, BWG, FI, and feed efficiency. Litter quality including litter pH, litter moisture, and litter nitrogen and tibia characteristics including breaking strength were not affected by dietary Ca concentrations. In conclusion, decreasing concentrations of Ca from 1.0 to 0.5% in diets containing 0.35% NPP and phytase (1,000 FTU/kg) have positive effects on growth performance of starter broiler chickens, but little effects on litter quality and tibia characteristics.