Background:Bladder cancer (BC) is the most common malignant tumor affecting the urinary system and is ranked as the tenth most frequently diagnosed malignancy worldwide. Apolipoprotein A1 (ApoA-I), a key component of high-density lipoprotein (HDL), plays a vital role in maintaining cholesterol homeostasis. Numerous studies have highlighted the crucial involvement of apolipoprotein A1 (APOA1) in tumor growth, invasion, and metastasis. This study aimed to evaluate the ratio of APOA1 in urine to serum among patients diagnosed with bladder cancer and explore the role of changes in this biomarker. Materials and Methods: A total of 56 paired blood and urine samples were obtained from bladder cancer patients. The participants included both genders, with an average age of 65.24 ± 10.40years. Additionally, 56 samples from healthy individuals served as controls. Apolipoprotein A1 levels in serum and urine were quantified using the ELISA technique. Results:The mean concentrations of apolipoprotein A1 in serum and urine in the bladder cancer group were significantly elevated compared to the control group with p-values of <0.01. A moderate positive correlation was observed between serum and urine apolipoprotein A1 concentrations (r=0.49, p<0.01). Conclusion:The elevated levels of serum and urine apolipoprotein A1 observed in bladder cancer patients suggest their potential use as biomarkers for early detection of the disease. However, urine apolipoprotein A1 appears to be a more reliable biomarker compared to serum levels, owing to its stronger association with bladder cancer and reduced interference from other medical conditions.