Two experiments were conducted on commercial layer hens to study the effects of dietary supplementation with two levels of 25-hydroxycholecalciferol (25(OH)D₃) and two levels of calcium pidolate (with or without 25(OH)D₃) on production performance and egg quality. Experiment 1 was conducted using 90 Hy-Line Brown layer hens from 19 to 80 weeks of age and commenced in November 2012. Birds were divided into three groups of 30 hens as follows: group A (control group) fed with normal commercial layer mash feed, and groups B and C (treated groups) fed with normal commercial layer mash feed plus 0.5 g of 25(OH)D3 [premix (68.9 μg 25(OH)D₃)] per kg of feed and 1 g of 25(OH)D₃ [premix (137.8 μg 25(OH)D₃)] per kg of feed, respectively. Experiment 2 was conducted using 147 Lohmann Brown layer hens from 21 to 80 weeks of age and commenced in March 2014.