The liquid polyester hexylsubstituted poly(lactic acid) (hexPLA) was investigated toward its suitability as an excipient for parenteral sustained-release formulations. HexPLA can be synthesized in pharmaceutical quality by a direct polycondensation method. The resulting small molecular weight polymers fulfill the basic requirements for a parenteral excipient, like sterilizability and injectability. Small lipophilic molecules are soluble in the hexPLA polymer matrix to a high extent, while hydrophilic peptides and proteins form suspension formulations, which can be prepared by a one-step cryo-milling-mixing method. The degradation and release characteristics of these formulations are controllable via the polymer molecular weight and drug loading. Small molecule solutions released the active substance over several days and for suspension formulations release periods of up to 6 months in vivo were achieved. Furthermore, the matrix protected the incorporated therapeutic protein from the environment and released it in its bioactive form, rendering hexPLA interesting as parenteral sustained-release excipient.