In the process of syngas bioconversion into high value-added chemicals, the presence and impact of impurities must be acknowledged. The present review aims to summarize the progress regarding the effects of various impurities on the syngas fermentation, with the focus on impurity formation in gasification, its inhibition on syngas conversion and influential mechanism. The production of impurities is influenced by various parameters in the gasification process, but substance characteristics is the most relevant factor on impurities composition and concentration. The inhibitory threshold of H