Bismuth subcarbonate (BiO)2CO3, sometimes written Bi2O2(CO3) is a chemical compound of bismuth containing both oxide and carbonate anions. Bismuth is in the +3 oxidation state. Bismuth subcarbonate occurs naturally as the mineral bismutite. Its structure consists of Bi-O layers and CO3 layers and is related to kettnerite, CaBi(CO3)OF. It is light sensitive.
It is highly radiopaque and for example is used as a filler in radiopaque catheters which can be seen by x-ray. In modern medicine, bismuth subcarbonate has been made into nanotube arrays that exhibit antibacterial properties. It is also used in fireworks  to make Dragon's eggs. It is a constituent of milk of bismuth which was a popular digestive tract panacea in the 1930s
Bismuth subcarbonate may be harmful if swallowed. It may irritate the respiratory and gastrointestinal tract.