The problem of improving the delamination resistance and toughness of laminate fiber-reinforced composites especially for the drop-off structure is receiving considerable attention with the increasing need and application in industries. A hot melt-bonding process is developed to bond glass fabric laminates and the thermoplastic (TP) polysulfone (PSU) interleaf prior to the vacuum assisted resin transfer molding (VARTM) of laminate composites. The TP interleaf is heated above the glass transition temperature to reduce the viscosity when penetrating deeply into the glass fiber fabric. Mechanical tensile testing is performed to quantify the effects of the penetration depth on composite delamination resistance and composite toughness under different melt-bonding temperatures. Crack paths are observed by optical microscopy to characterize the crack propagation and arrest mechanism. Postmortem high-resolution imaging of the fracture surfaces is used to characterize the toughening mechanism of the TP interleaf reinforcements by using scanning electron microscopy (SEM). With deep penetration of the interleaf into the fiber bundles, cracks arrested within the penetration region improve the toughness by avoiding the cracks to reach the weak interface between interleaf and epoxy.