Totok clams (Geloina sp.) are one of the estuarine biotas that can be found in Serayu river, Bulupayung Village, Cilacap Regency. People of Bulupayung only take the clam's flesh which causes abundant shell waste that has not been untapped well. The results of ash level analysis showed that the shell contained 0,48% sodium (Na) and 3,11% calcium (Ca). The calcium is useful for poultry to meet their mineral need to form their eggs. Therefore, this research aimed to find out the effects of adding micro-calcium flour from Totok clams shells to the characteristics of duck eggs. This research used a Completely Randomized Design with the treatment of P0 (control), P1 (3,65% of shells from156 gr of feed), P2 (4% of shells from 156 gr of feed), and P3 (5% of shells from 156 gr of feed) with two repetitions. The observed parameters included the egg weight, the egg whites weight, the egg yolks weight, and the eggshells weight. The data were then analyzed using ANOVA on the level of 95% and continued with Duncan Multiple Range Test. The results show that adding micro-calcium flour from the clams shells can increase the weight of the egg, egg white, egg yolk, and eggshell significantly (p<0,05). P0 was significantly different in all parameters with various treatments.This proved that micro-calcium flour from Totok clams shells can be used as a feed mixture for ducks with an optimal dosage of 5%/156 gr of feed (P3).