Ninety six beak-trimmed 72 week-old Lohmann Brown hens were randomly divided into four equal groups. Each group comprised 4 replicates. Isoenergetic and isonitrogenous experimental diets contained low calcium (3.5%); optimum calcium (4.2%); low Ca (3.5% Ca)+1% Clinoptilolite (CLP); low Ca (3.5% Ca)+2% CLP. Data were collected biweekly and the experiment lasted 6 weeks. Egg production, feed consumption, feed conversion ratio, egg weight, tibia Ca. P. ash and eggshell thickness were not affected by addition of CLP to the diets (p>0.05). There were no significant differences in egg shell strength and ash when data were analyzed individually in measurement periods (74(th), 76(th) and 78(th) weeks). However, according to pooled data (74(th)-78(th) weeks), eggshell strength was increased (p<0.05) only by 2% CLP supplementation versus low Ca (3.5%) diet, and shell ash was significantly increased by 2% CLP supplementation compared with the other diets. The damaged egg ratio on 1% and 2% CLP diets was significantly decreased between 76-78 weeks' data when compared with the low Ca diet. However; damaged egg ratio on the 2% CLP diet was significantly decreased when pooled data (74-78) were compared with no CLP diets. The differences in marketable egg ratio paralleled damaged egg ratio. The plasma calcium level at the end of experiment was increased on the 2% CLP diet when compared with the low Ca (3.5%) diet (p<0.05). Furthermore, at the end of the experiment a marked decrease of manure moisture was observed on both CLP diets (p<0.01). In conclusion. Clinoptilolite (2%) supplementation to layer diets tends to improve eggshell quality and manure dry matter (1% and 2% CLP) after six weeks.