This study evaluated the effects of dietary supplemental levels and sources of manganese (Mn) on performance, eggshell quality, ultrastructure, and components in laying hens. A total of 1,080 46-wk-old Jing Brown hens were fed a basal diet (Mn, 32.7 mg/kg) for 2 wks laying and then randomly allocated to 9 groups that were fed a basal diet (control) or the basal diet supplemented with inorganic (MnSO4·H2O) or organic (amino-acid-Mn, 8.78%) Mn at 40, 80, 120, or 160 mg per kg of feed for 8 wks. Each group had 8 replicates of 15 hens. The results showed that dietary Mn supplementation did not affect the performance of hens (P > 0.05). Dietary Mn supplementation resulted in linear and quadratic increases of breaking strength and thickness in both inorganic and organic forms (P < 0.05), but fracture toughness increased quadratically only in organic groups (P < 0.05). Linear and quadratic effects on effective and mammillary thickness were observed with Mn supplementation from inorganic and organic sources (P < 0.05), and lower mammillary thickness was observed in organic groups (P < 0.05). However, the width of mammillary knobs decreased quadratically only with the supplementation of organic Mn (P < 0.05). Dietary Mn supplementation had a quadratic effect on the shell Mn content in both inorganic and organic forms (P < 0.05). Linear and quadratic effects on the content of sulfated glycosaminoglycans (GAGs) were observed only in calcified eggshell with inorganic Mn supplementation (P < 0.05), while the supplementation of organic Mn had a quadratic effect on sulfated GAGs content in both calcified eggshell and membranes (P < 0.05). Overall, dietary Mn supplementation, regardless of the source, could increase breaking strength and thickness by improving the ultrastructure, which partly results from increased sulfated GAGs content in the eggshell. Moreover, the supplementation of organic Mn could increase fracture toughness by decreasing the width of mammillary knobs, which is partially due to increased sulfated GAGs content in the membranes.