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We propose high-resolution ACS imaging to resolve the nature of a newly discovered double quasar system at z=5.66 comma J2037-4537 comma which could be either a close quasar pair or a gravitationally lensed quasar. Ground-based observations show that J2037-4537 consists of two point sources separated by 1.26d_comma comma both of which have a spectrum of a z=5.66 quasar. However comma limited by the seeing comma it is uncertain whether the lens galaxy exists. The two components are either a physical quasar pair or lensed images of the same quasar. In the former case comma J2037-4537 will be the highest redshift quasar pair comma which will place strong constraints on the model of AGN formation and evolution comma and will enable follow-up observations to study galaxy mergers that trigger quasar activity comma to probe the kpc-scale structure of the intergalactic medium at z>5.5 for the first time comma and to search for protocluster traced by the quasar pair. In the latter case comma J2037-4537 will be the second lensed quasar discovered at z>5 and will be an excellent case study for the high-z SMBH population comma aided by lensing magnification. With an Einstein ring size of 1.26d_comma comma J2037-4537 will provide the best chance to detect the stellar light from a quasar host galaxy at high-z. The key to distinguishing the two scenarios is to detect the lens galaxy. However comma the lens galaxy is likely only 0.3d_comma away from the fainter quasar image comma which is impossible to get resolved from the ground. Here we propose to use ACS-WFC to confirm (or rule out) the presence of the foreground lens galaxy. With a modest request of 1 orbit comma we will identify J2037-4537 as either a lensing system or a close quasar pair and prepare for follow-up observations.