Since the last decade, most research focus in the fields of science and engineering has been dramatically shifted toward the same fashion from the investigation of traditional macroscale properties of materials to their atomic scale level (or called nanoscale). It is believed that the mechanical, electrical and thermal properties of materials, at their nanoscale level are totally different with that measured at macro and micro scale levels due to an assumption of their perfect atomic architectures, i.e., no-defect among atoms. In such circumstance, the strength of the materials can therefore reach to their ideal level since the maximal bonding energies among the atoms can be achieved. Recently, numerous researches have been focused on using nanomaterials as reinforcements to strengthen polymer-based composites for space and bio-engineering applications. Carbon nanotubes are the most common types of nanomaterials that have been used to mix with polymer to form nanocomposites. The nanotubes possess superior mechanical strength and electrical conductivity at specified chiral arrangements for producing high strength conductive polymers. In this paper, a critical review, based on the works done by authors and other researchers on the properties and applications of the carbon nanotubes for space and bio-engineering applications is given. Their advantages and disadvantages on some particular applications are also discussed in detail.