Novel hyperbranched polyesteramides have been synthesized from diethanolamine and maleic anhydride with ethylene glycol as a core monomer. No gelation occurred in the melt polymerization when diethanolamine and maleic anhydride were used in equimolar amount in the feed and when content of ethylene glycol was varied. Obtained products were soluble in water and in organic solvents such as NMF. The obtained polymers were characterized by using IR and NMR spectroscopies as well as GPC. It was suggested that the hyperbranched polyesteramides formed via a mechanism of a combination of esterification and addition reactions. The addition of a hydroxyl group to the - CH=CH- in maleic anhydride unit results in a formation of CH methine group. The ratio of -CH=CH- to CH in the polymers were estimated from 1H NMR spectrum as 0.140, 0.155, 0.175, 0.190 and 0.204 for polymers P1 to P5, respectively as the content of ethylene glycol charged decreased. The molecular weights and their polydispersities showed reverse dependences on the feed ratio of ethylene glycol to diethanolamine. The rheological properties of the polymers in aqueous solution were also examined. The polymers exhibit a steady increase of intrinsic viscosity with increasing molecular weight, and the Mark-Houwink exponent for these polymers is 0.26, which is much lower than 0.5 and suggested that these polymers possess a highly branched architecture. The polymer solutions showed a Newtonian behavior with steady shear viscosities independent of shear rate, which indicated the absence of a physical entanglement.