Abstract: A para-phenylene sulfide block copolymer consisting essentially of a recurring unit (A) ##STR1## and a recurring unit (B) ##STR2## said recurring units (A) being present in the form of a block of 20 to 5,000 units of (A) on the average in the molecular chain, the mol fraction of the recurring units (A) being in the range of 0.50 to 0.98, the block copolymer having a melt viscosity (.eta.*) of 50 to 100,000 poise as determined at 310.degree. C. at a shear rate of 200 sec.sup.-1 and having: (a) a glass transition temperature (Tg) of 20.degree. to 80.degree. C., (b) a crystalline melting point (Tm) of 250.degree. to 285.degree. C.