The study of Pt nucleation on Au(111) deposited via surface limited redox replacement of underpotentially deposited Cu monolayer is presented. Series of Pt deposition experiments were performed where starting coverage of an underpotentially deposited Cu monolayer varied from 0 to 1. Exsitu Scanning Tunneling Microscopy and statistical image processing are used to characterize the morphology of deposited Pt monolayers. The Pt nucleation density and the average size (area) of Pt nanoclusters is used as the main descriptors of Pt monolayer morphology. Results are discussed within the framework of analytical model developed to describe qualitatively our data. The relevance of our work for design of Pt monolayer catalyst is illustrated studying the CO electrosorption on Pt monolayers with different nucleation densities and average size of Pt nanoclusters. (C) 2014 The Electrochemical Society. All rights reserved.