Polylactic acid is one of the most promising bio-based candidates for the substitution of the traditional petroleum-based polymers. However, PLA has numerous drawbacks (e.g. brittleness and low melt strength) which limit its use in different applications such as packaging. In this work, we propose the concept of in situ microfibrillation as a means to improve the properties of PLA/nylon-6 blends. PLA/nylon-6 blends were produced by a simple melt extrusion process followed by a hot stretching step which transformed the nylon-6’s spherical domains into microfibrils with diameters of nearly 200 nm. Morphological characterizations of the compression molded samples confirmed that the nylon-6 phase was in the form of fully-stretched and well-dispersed microfibrils. The inclusion of the nylon-6 phase, in both spherical and microfibrillar shapes, improved the crystallization behavior of the PLA while the improvement was more substantial in the case of blends with microfibrillar nylon-6 domains. This improvement in the crystallization behavior of PLA led to an increase in its tensile properties. Crucially, it was observed that both the stiffness and the deformability of the PLA were improved which led to a significant increase in its tensile strength. Studying the linear viscoelastic behaviors and the extensional viscosities of the compounds showed that the physical entanglement of the long nylon-6 microfibrils led to their rheological percolation (gelation), which substantially improved the PLA’s melt strength and elasticity. The gelation occurred at a nylon-6 concentration of nearly 2.5 wt.%. The facile and cost-effective process which was used for the production of the microfibrillar PLA/nylon-6 blends makes this approach ideal for the improvement of PLA as a competitive candidate in the packaging industry.