<P><B>Abstract</B></P><P>Biological mycelia pellets, which are formed spontaneously in the process of <I>Aspergillus niger</I> Y3 fermentation, were explored as carrier for immobilization of <I>Clostridium</I> sp. T2 to improve hydrogen production. Batch fermentation tests showed that optimal dosage and size of mycelia pellets for hydrogen production were 0.350 g 150 ml<SUP>−1</SUP> medium and 1.5 mm. Under these conditions, hydrogen production with immobilized cells on mycelia pellets was further investigated in continuous stirred-tank reactor (CSTR) with hydraulic retention time (HRT) ranging from 12 to 8 h. It obtained that the maximum hydrogen production rate reached 2.76 mmol H<SUB>2</SUB> L<SUP>−1</SUP> h<SUP>−1</SUP> at 10 h HRT, which was 40.8% higher than the carrier-free process, but slightly lower than the counterpart immobilized in sodium alginate with the value of 3.15 mmol H<SUB>2</SUB> L<SUP>−1</SUP> h<SUP>−1</SUP>. SEM observation showed that abundant cells were closely adhered to mycelia pellets. The present results indicate the potential of using mycelia pellets as biological carrier for enhancing hydrogen production.</P> <P><B>Highlights</B></P><P>► Mycelia pellets were explored as carrier to improve hydrogen production. ► Optimal mycelia pellets dosage and size were tested. ► Continuous process demonstrated the immobilization quality of mycelia pellets. ► Mycelia pellet is an alterative carrier for improving hydrogen production.</P>