Moisture absorbent core sheath composite yarn

A moisture absorbent core sheath composite yarn having a sheath portion polymer that is a polyamide and a core portion that is a thermoplastic polymer, and having a moisture absorbance/desorbance (ΔMR) of 5.0%, wherein the ΔMR maintenance rate after 20 washes is 90-100%. A core sheath composite fiber having high moisture absorbance, being more comfortable than natural fibers, and having wash resistance with moisture absorbance that stands up to real use and color fastness is provided.