A useful biomarker for detecting cardiac amyloidosis (CA) has not been fully established. We aimed to investigate the utility of several biomarkers to detect CA in patients with amyloid light-chain (AL) amyloidosis.We examined the plasma levels of B-type natriuretic peptide (BNP), N-terminal fragment of the pro-brain natriuretic peptide (NT-proBNP), high-sensitivity cardiac troponin T (hs-cTnT), serum amyloid A, and the difference between kappa and lambda free light chain (dFLC) between CA patients (n = 30, 47.6%) and non-CA patients (n = 33, 52.4%). Levels of BNP were significantly higher in the CA group compared to the non-CA group (1200.0 versus 224.0 pg/mL, P = 0.001). From the ROC analysis, the sensitivity and specificity of BNP for detecting CA (with a cut-off value of 412 pg/mL) were 83% and 70%, respectively, and the area under the receiver operating curve was 0.75 (95% CI 0.61-0.90, P < 0.001) in all AL amyloidosis patients (n = 63). In contrast, other markers such as NT-proBNP, hs-cTnT, serum amyloid A, and dFLC were not useful for detecting CA in AL amyloidosis patients. Additionally, in the Cox proportional hazard analysis, BNP was a predictor of all-cause mortality (hazard ratio 3.266, 95% confidence interval 1.498-7.119, P = 0.003).BNP is a useful biomarker for detecting cardiac involvement and predicting prognosis in AL amyloidosis patients.