A thermoplastic cellulose derivative composition of the present invention contains,
as a main component, a cellulose ester having an aliphatic polyester side chain
having a repeat unit having 2 to 5 carbon atoms, wherein a rate of heating loss
at 200 C. is 5 wt % or less, a melt viscosity at 200 C. and 1000 sec-1
is 50 to 300 Pasec, and a melt tension at the time of take-up at 200
C. and 100 m/min is 0.1 to 40 mN. The present invention can provide excellent fiber
products by melt spinning of the composition.