Predicting thrombolytic susceptibility to recombinant tissue plasminogen activator (rt-PA) a priori could help guide clinical decision-making during acute ischemic stroke treatment and avoid adverse off-target lytic effects. The composition and structure of clots impact their mechanical properties and rt-PA thrombolytic efficacy. The goal of this study was to determine the relationship between clot elasticity and rt-PA thrombolytic efficacy in vitro. Human and porcine retracted and unretracted clots were fabricated in glass pipettes. Clots were embedded in agar phantoms, and their Young’s moduli were estimated using single-track-location shear wave elasticity imaging. The rt-PA thrombolytic efficacy was evaluated in vitro using the percent clot mass loss. The Young’s moduli of unretracted porcine and human clots (1.68±0.18 kPa and 0.72±0.13 kPa, respectively) were significantly lower (p<0.05) than those of retracted porcine and human clots (4.96±1.07 kPa and 3.38±1.82 kPa, respectively). The percent mass loss of unretracted porcine and human clots (28.9±6.1% and 45.2±7.1%, respectively) were significantly higher (p<0.05) than those of retracted porcine and human clots (10.9±2.1% and 25.5±10.0%, respectively). The results revealed a linear inverse correlation between the Young’s moduli and percent clot mass loss (R2 = 0.95, p = 0.025), suggesting that clot stiffness may serve as a surrogate metric for rt-PA thrombolytic susceptibility.