Biohydrogen production is considered as one of the most promising alternative processes to produce hydrogen due to its effectiveness, renewability, and environmental friendliness compared to the conventional way, such as thermochemical and electrochemical methods. Biohydrogen production via photofermentation produces hydrogen by photo-decomposing organic matters through the nitrogenase of photosynthetic bacteria. Despite its advantages, high energy requirement during nitrogenase-catalyzed reaction and low biohydrogen production efficiencies in the reality have become the foremost concern in a large scale application of photofermentation. Thus, an improvement of biohydrogen yield and light conversion efficiency is necessary to increase the feasibility of photofermentation. One of the simplest ways to improve photofermentation is by adding suitable chemical enhancer. Various studies have shown that an addition of some chemicals, such as iron, molybdenum, ethylenediaminetetraacetic acid (EDTA), vitamins, buffer solution, and others chemicals could increase the biohydrogen production rates and yields by a significant value. However, an addition of other chemicals, such as nickel ions, diphenylene iodonium, dimethylsulphoxide, and copper ions, might cause an adverse effect on the process. Addition of EDTA, molybdenum, ethanol or yeast may inhibit the photofermentation process, depending on the type of bacteria and substrates used during photofermentation process, as well as the concentration of the added chemicals. Hence, the importance and effects of chemicals addition on photofermentative biohydrogen production were discussed in this review paper.