High bilirubin in lung cancer is caused by gradual progress of disease and abnormal physical condition, which may be caused by liver metastasis of tumor, obstruction of biliary system and hemolysis. Bilirubin is a pigment formed by metabolic transformation of hemoglobin in red blood cells, including direct bilirubin and indirect bilirubin. 1. Increased direct bilirubin is mainly seen in obstructive jaundice, hepatocellular jaundice, hepatocellular carcinoma, pancreatic head carcinoma, cholelithiasis, cholangiocarcinoma and so on. Therefore, if lung cancer is combined with intrahepatic metastasis, lymph node metastasis, etc., it may compress the bile ducts or damage the liver cells, resulting in elevated direct bilirubin; 2. Increased indirect bilirubin, which is common in acute jaundice hepatitis, acute hepatic necrosis, chronic active hepatitis, cirrhosis, hemolytic anemia, blood group incompatibility transfusion, hepatocellular jaundice, severe scald, septicemia, malaria, hyper-splenism, pernicious anemia, anemia with impaired production of beads proteins, lead poisoning, pharmacological jaundice, somatic jaundice and so on. Therefore, elevated bilirubin can also occur if lung cancer patients are combined with hepatitis, cirrhosis or develop other related diseases mentioned above. In conclusion, elevated bilirubin in lung cancer patients may be due to the disease itself, or may be due to other combined diseases. It is recommended to go to regular hospitals to evaluate the condition and follow the doctor’s instructions to avoid delaying the condition.