A new approach for evaluating the dilational modulus of an adsorbed protein film was proposed in this study; wherein, the air-water interface of Bovine serum albumin (BSA) aqueous solution was not subjected to a forced perturbation. The approach involved: (i) monitoring the relaxations of surface tension (ST), surface area (SA), and ambient/solution temperature of aqueous bovine serum albumin (BSA) solution using a pendant bubble tensiometer and (ii) detecting the numerous minute and low-frequency interfacial perturbances in the SA and ST relaxations (resultant from the minute variations in ambient temperature) at the latter stages of BSA adsorption process. For these perturbances, their surface dilational rate (dlnA/dt) and rate of ST change (dγ/dt) were determined, and then the dilational modulus (E = dγ/dlnA) was obtained from the slope of the linear best-fit in the plot of dγ/dt vs dlnA/dt. Using this approach, the dilational modulus of the adsorbed BSA film at a concentration of 0.052 and 15 (10⁻¹⁰ mol/cm³) was found to be 43 and 30 mN/m, respectively.