Taiwan produces an average of 160,000 metric tons of discarded oyster shells each year, of which 26,000 metric tons are not handled properly. Discarded oyster shells not only take up space, have low economic value, and have concerns about environmental pollution. In the past, about 70% of discarded oyster shells were used in feed, compost and cultivation media, and their added value was not high. With the rise of the pet market, pet supplies do have their potential for development. This project uses oyster shell modification technology to develop oyster shell cat litter. The water absorption of oyster shell cat litter is 164%, which is better than commercially available crystal litter, and has the advantages of odor absorption, low price and natural ingredients. But it has no antibacterial effect like the commercial products. In addition, the number of cat litter dust has been adjusted to the market. The results of this research and development are only prototypes and there is still room for adjustment. When the technology matures in the future, it can impact the pet market, increase the added value of oyster shells, and solve the problem of environmental pollution caused by the stacking of discarded oyster shells in order to implement sustainable operations in a circular economy.