A process for the production of polyester polyurethane elastomeric fibers having improved humid aging resistance which comprises the steps of reacting a polyester diol with an excess molar amount of an organic diisocyanate to prepare a urethane prepolymer having terminal isocyanate group at both ends thereof; extending the chain of the prepolymer with a bifunctional active hydrogen compound and 0.5 to 10.0 mole % of a diaminosilyl compound based on the total amount of the bifunctional active hydrogen compound during or after preparation of the prepolymer to obtain a polyurethane; spinning the polyurethane into fiber; and crosslinking the polyurethane during or after spinning.