Blends of low density polyethylene (LDPE) or polyamide 6 (PA6) with two types of functionalized polyethylenes compatibilizers, namely: poly(ethylene-co-acrylic acid) (Escor5001 by Exxon) and ethylene-glycidylmethacrylate copolymer (Lotader GMA AX8840) in the LDPE/compatibilizer or PA6/compatibilizer composition 80/20 w/w, have been prepared. The morphology, crystal structure, isothermal crystallization behavior and microhardness of the blends have been studied by optical and electron microscopy, DSC, WAXS and microhardness tests. The peculiarities in the new characteristics of the blends investigated have been revealed. The isothermal crystallization rate of both LDPE and PA6 decreases in the presence of the two types of compatibilizers. The crystallization enthalpy only of the LDPE blends is a function of the crystallization temperature. In the presence of the compatibilizer, PA6 or LDPE crystallize into spherulites with dimensions smaller than those of the corresponding neat polymers. The crystallites dimensions and degree of crystallinity do not change in LDPE/compatibilizer blends, while there are strong reductions of the degree of crystallinity and the crystallites dimensions of the components in the PA6/compatibilizer blends if compared to those of the neat polymers. The microhardness values of the PA6/compatibilizer blends are lower than the corresponding additive values, while the microhardness of LDPE/compatibilizer blends corresponds to the additive values. The results have been interpreted by different types of interactions between the functionalized polyethylenes and LDPE or PA6, correspondingly. The results indicate that the compatibilization efficiency of Escor towards PA6 is higher than that of Lotader.