In this study, a sensitive technique (Broadband Cavity Enhanced Absorption Spectroscopy (BBCEAS)) is employed for measuring the absorption of thin films deposited onto a glass substrate. A thin film of the biological solution such as Lyophilied Bovine haemoglobin is deposited on glass microscope coverslips. Drop coating method was used to deposit a thin film over the microscope coverslips. The number of passes is calculated: 612 passes for the high reflectivity mirror were obtained. The best measurements are made with the mirror set of reflectivity of (R≥ 0.99) which produced an αmin value of 0.0043 cm-1 and LOD of 1.9×10-7M.