Viscous poly(ortho-ester)s (POE), synthesised by a transesterification reaction between a substituted orthoacetate and a triol have been shown to be bioerodible polymers and are currently under investigation as a drug carrier material. Main efforts of the polymer development so far have been focused on a polymer prepared of trimethyl orthoacetate and 1,2,6-hexanetriol. The present investigation describes the synthesis and characterisation of an analog polymer. By replacing the 1,2,6-hexanetriol with 1,2,10-decanetriol, a higher molecular weight aliphatic triol, the physio-chemical characteristics of the polymer can be changed. The new POE, prepared by a transesterification reaction of trimethyl orthoacetate and 1,2,10-decanetriol is less viscous and more hydrophobic. Due to the decreased viscosity the polymer is easier to use for injectable applications and due to the increased hydrophobicity, the release rate of the chosen compound, the water-soluble 5-fluorouracil (5-FU) is slowed down, compared to the POE described earlier.