Blends were made by solution and melt-mixing fatty-acid-modified dendrimers with various polyolefins. Small-angle neutron scattering (SANS) was used to determine the miscibility of the blends. Poly(propylene imine) (PPI) dendrimers G1, G3, and G5 [DAB-dendr-(NH2)gamma] with gamma = 4, 16, and 64, were reacted with stearic acid or stearic acid-d(35) forming amide bonds. The modified dendrimers were then blended with high-density polyethylene (HDPE), high-density polyethylene-d(4) (HDPE-d(4)), low-density polyethylene (LDPE), amorphous polypropylene (PP), or an ethylene-butylene copolymer (E-co-B). Limiting power law behavior shows that all of the blends are immiscible. It is likely that the dendrimers form a second phase, being finely dispersed, but thermodynamically immiscible.