Chitinases are occurring in organisms that need to either reshape their own chitin or dissolve and digest the chitin of other invading fungi and animals. Chitin has not been found in mammals. Nevertheless, several mammalian Danshensu proteins with homology to fungal, bacterial, or plant Chitinase have been identified. All Chitinases have been recognized to play important roles in self-defense against pathogens. Most recently, however, some Chitinases have been found to appear in response to environmental stresses, such as cold, drought, and high salt concentration. Other Chitinases are reported to participate in important physiological processes of plants, such as embryogenesis and ethylene synthesis. The variable effectiveness of specific Chitinases against different pathogens and the existence of microbial Chitinase inhibitors led to the hypothesis that Chitinases may coevolve with fungi in response to variation in pathogen defenses against chitinolytic activity. The majority of protein sequences is aperiodic and usually has globular 3D structures carrying a number of various functions. The foremost efforts of researchers were devoted to these types of proteins and as a result, significant progress has been made in the development of bioinformatics tools for their analysis. However, proteins also contain a large portion of periodic sequences representing arrays of repeats that are directly adjacent to each other. Intragenic duplications of genetic material have important biological roles because of their protein sequence and structural consequences. Bioinformatics tools are important for analysis of protein repeats with emphasis on the sequences, 3D structures, and sequence�Cstructure relationship as well as highlighting successful strategies for the prediction of the protein structure. These tandem repeats are considerably diverse, ranging from the repetition of a single amino acid to domains of 100 or more residues. They are ubiquitous in genomes and occur in at least 14% of all proteins. Before analysis of repeats, it just needs to score protein sequences in multiple sequence alignment. Common methods for detection of similarity depend on pairwise alignment of sequences. The abundance of natural structured proteins with tandem repeats is inversely correlated with the repeat perfection. The chance to find natural structured proteins in Protein Data Bank increases with a decrease in the level of repeat perfection. When a certain threshold of the conserved Senegenin residues in the repeat is exceeded, the repetitive regions of proteins are predominantly disordered and the main reason of residue conservation in tandem repeats may due to the change from a structural to an evolutionary one. Hence, internal repeats in Chitinase involved in diversification of Chitinases with different structural and functional properties and it may also play role in quick evolution of Chitinase in all organisms. Repetitive sequences apparently formed after the prokaryotic-eukaryotic divergence by a mechanism with weak length-dependence such as recombination. Repetitive proteins evolve quicker than non-repetitive proteins. Protein repeats have highlighted the multi-functionality of repeat types, their structural differences, and their proliferations in different evolutionary lineages.