Ribozymes are catalytic molecules that cleave ribonucleic acid (RNA) at specific sequences (Gesteland et al. 2006). RNA is the nucleic acid produced in the transcription process; when deoxyribonucleic acid (DNA) anneales, it transcribes into a linear-stranded molecule called RNA. In order for RNA to synthesize proteins, it requires catalytic enzymes to carry out certain chemical reactions. In the past it was thought that all chemical reactions were catalyzed by protein enzymes; however, in the 1980s this hypothesis was disproved when Thomas Cech and Sydney Altman discovered that RNA is capable of carrying out self-catalyzing activities which were called ribozymes because they perform functions similar to those of protein enzymes (Jaeger, 1997). Although RNA ribozymes lack the diversity of functional groups found in protein enzymes, they are able to carry out their own catalytic reactions due to their tendency to fold into a 3D structure and form helices via the role of Watson-Crick base pairing (Kiehntopf et al. 1995). Ribozymes now play a vital role in understanding biochemistry, as they have the ability to catalyze some of the most important chemical reactions such as RNA splicing and peptide synthesis, for example ribozymes can accelerate phosphoryl transfer chemical reactions by 1011 folds. This review will describe the structure, sources, and applications of ribozymes. So far, several naturally occurring ribozymes have been identified; these are divided into three distinct classes. First, self-splicing introns, which fall into groups I and II respectively depending on their structure and recognition sequences. The self-splicing group I intron was the first ribozyme a b...... center of paper ...... in cells, the location of ribozymes in cells as well as the site of messenger RNA sorting ( James and Gibson, 1998). Ribozymes are currently believed to hold much promise for the future development of gene therapy as they have the ability to splice and cleave any target RNA sequence. Seven natural ribozymes are known, and several artificial ribozymes have been created. These artificial ribozymes are used as therapeutic agents to target aberrant gene expression in many lethal diseases such as cancer. The limitation of artificial ribozymes is mainly due to the difficulty in their delivery to target cells. Therefore, further research needs to be conducted to thoroughly study the organization and structures of natural RNA ribozymes to obtain successful artificial ribozymes that have complex function in the future..