We study Ultra-high energy cosmic ray (UHECR) as an effective tool to probe new physics interactions thanks to its high energy beyond the currently available accelerator energies. In particular, we consider electroweak sphaleron and microscopic black hole as some of the new physics examples generating genuinely large multiplicities resulting in various observable effects. We examine the characteristic features of UHECR-nucleon collision events in the atmosphere and discuss the search strategies of such events at Telescope Array Experiment (TA) and Pierre-Auger Observatory (Auger).