The motivation of this thesis is to investigate the role of multi-walled carbon nanotube (MWCNT) in enhancing the interlaminar shear strength (ILSS) of hybrid composites. The objective of this thesis is to understand the relationships between processing history, material variability, matrix properties, glass fiber/matrix interface properties and their correlations with interlaminar shear strength of hybrid composites. The interlaminar shear strength (ILSS) of hybrid composites made from glass fiber and multi-walled carbon nanotube (MWCNT) modified epoxy is compared with that for unmodified epoxy/glass fiber composites (control). By combining the techniques of high speed mechanical stirring and ultrasonic agitation, 0.5% MWCNT by weight were dispersed in epoxy to prepare a suspension. Composites were manufactured by both injection double vacuum-assisted resin transfer molding (IDVARTM) and the flow flooding chamber (FFC) methods. Compression shear tests (CST) were conducted on the manufactured samples to determine the ILSS. The effect of processing history and batch-to-batch variability of materials – glass fiber preform, resin and carbon nanotubes – on the ILSS of samples made by both techniques was investigated. Statistical comparison of the measured ILSS values for hybrid composites with the control specimens clearly show that hybrid composites made by the FFC process resulted in significant ILSS enhancement relative to the control and the IDVARTM specimens. After it was established that the FFC process improved the ILSS, the effect of functionalizing the nanotubes was explored. Multi walled carbon nanotubes (MWCNT) were oxidized by acid treatment and heated with triethylene tetra amine (TETA) to obtain amino functionalized MWCNTs (f-MWCNT). Hybrid composites with f-MWCNTs were manufactured using FFC technique and control samples were fabricated using the same E-Glass fiber mat and unmodified epoxy resin subjected to the same processing history. CST results show 41% increase in ILSS for hybrid composites containing p-MWCNTs and a 61% increase for samples containing f-MWCNTs relative to the control samples without MWCNT. Tests of the epoxy preparations were conducted to investigate if the increase in ILSS is due to an increase in the shear strength of epoxy containing nanotubes or to strengthening of the interface between the glass fiber and the epoxy containing nanotubes. Small punch test and miniature shear punch tests were conducted to characterize the young’s modulus, yield shear strength and ultimate shear strength of the neat epoxy and MWCNT epoxy composites and micro droplet tests were conducted to characterize the interfacial shear strength, the strength of the fiber-matrix interface for both modified and unmodified matrix. The results indicate that the ILSS increase was due to the stronger interface bond due to the addition of nanotubes rather than any enhancement in the epoxy shear properties.