The effect of feeding varying dietary levels of limestone (LS) and periwinkle shell (PS) on laying perform-ance, egg characteristics, blood parameters and bone mineralization of hens was studied. A total of 108 sixteen-weeks-old pullets (weighing 1.2±2.00 kg) were allotted to 6 treatments with 3 replicate groups of 6 birds in each pen. The LS and PS were supplemented in the diets at three levels (3.00%, 3.75% and 4.50%) each for a period of 12 weeks. Birds fed 3.75% PS had the highest (P<0.05) feed intake and hen-day egg production with an improved feed conversion ratio. The inclusion levels of PS significantly (P<0.05) im-proved most of the external and internal egg quality parameters studied with the best result recorded among the laying hens fed 3.75% PS and 4.50% PS. Some of the blood parameters and bone mineralization were better (P<0.05) for hens fed 3.00% PS and 3.75% PS. On the other hand, the source of calcium and its lev-els had no significant effect on initial body weight, final body weight, total weight gain, average daily weight gain, egg weight, egg surface area, yolk height, yolk index, total protein, alanine aminotransferase, aspartate aminotransferase, bone phosphorus, tibia weight and dry defatted bone. Based on the results ob-tained from the present study, it was concluded that 3.75% PS was appropriate for laying hens without ad-verse effect on performance and the inclusion of PS in layer rations as calcium source is more beneficial than LS. تفاصيل المقالة