The prediction of functions of proteins in living organisms can be made based on its domain analysis, proteinprotein interactions, sequence comparisons, structure comparisons, and phylogenetic tree analysis. Domain analysis and protein-protein interactions are important tools of bioinformatics based on which annotation of conserved domain footprints on protein sequences can be ascertained which could serve as the first step towards characterizing protein function(s) in silicon. In the present investigation, the functionality of butyrylcholinesterase (BChE) was ascertained by employing domain analysis and protein-protein interaction(s) tools. We collected the sequence of BChE, established the domains of this protein using NCBI conserved domain database (CDD), and identified proteins that interact with it (BChE). Using this data, we identified proteins with similar domain, proteins with which it interacted, and annotated the function of BChE via sequence similarity. These studies revealed that BChE interacts with proteins: ubiquitin-conjugating enzyme, apoptosisantagonizing transcription factor, paraoxonase/arylesterase, pyruvate dehydrogenase protein X component, proteasome activator complex subunit 3, 4-trimethyl-aminobutyraldehyde dehydrogenase, and vacuolar proton translocating ATPase whose functions are known. Based on this information, it is predicted that BChE may have actions similar to those with which it interacts. Thus, by using domain analysis and protein-protein interaction(s) tools it may be possible to identify the functions of proteins whose action is unknown by annotating the conserved domain amino acid sequence of proteins whose function is known with those of the unknown.