We have examined the effect of reducing MoS3 in hydrogen in the range 450–800 °C on the properties of the resulting MoS2 catalyst. The appearance of rhombohedral MoS2 at 800 °C is disputed. Instead, an 'overreduced' catalyst containing some Mo metal and hexagonal MoS2 was formed. Catalytic activity in thiophene hydrodesulfurization was insensitive to pretreatment.