Experimental and theoretical results are reported on the dependence of melt viscosity on the molar mass of poly(diethylene glycol-co-succinic acid) (DEG-SA) in the nonentangled regime. A power law described the behavior with an exponent of 2.09 +/- 0.10 at 30-degrees-C and of 2.59 +/- 0.09 at 90-degrees-C. The modified Rouse theory was used to describe the relationship between melt viscosity and molar mass. The parameters related to the modified Rouse theory were determined by the WLF equation and the free-volume theory. The WLF parameters of various samples were checked at their T(g), which is the reference temperature. Results confirmed that the free volume and the monomeric friction coefficient (xi0) dominate the behavior of the melt. The agreement between the calculated and experimental melt viscosity is satisfactory.