<p>In this paper,we explore the cluster algebras for symbol letters or singularities of cosmological correlators in a conformally coupled scalar field theory. We show that the symbol letters for tree-level <i>n</i>-site ladder cosmological correlators are governed by <i>A</i>_{2(<i>n</i>−1)} cluster algebras. Additionally, we demonstrate that the symbol letters for one-loop bubble cosmological correlator are an union of two <i>A</i>₃ cluster algebras. The algebras relations of letters will provide an important tool to bootstrap analytic cosmological correlators.</p>