The main obstacle in directly reducing zinc sulfide concentrate in a commercial vertical retort is the difficulty to produce strong briquettes. The authors have successfully applied a new method to the preparation of strong briquettes which have satisfactory strength even after almost all the zinc sulfide in the concentrate has been reduced to zinc vapor. The method consists of mixing zinc sulfide concentrate with pulverized coal and calcium oxide, preheating and briquetting the mixture into a cylindrical briquette of 1.3cm in diameter, and then coking the briquette. Effects of mixing ratio, preheating temperature and time, particle sizes of concentrate, coal and calcium oxide on the strength of the briquette have been axamined. Sinze almost no sulfur has been observe to come out of the briquettes and also since they have considerably low specific resistance of 5.1Ω·cm, it has been suggested that the briquettes may be fed not only into a vertical retort but also into an electrothermic furnace without additional coke.