Background: Mixing in traditional algae culture system consumes intensive electricity. This should be replaced by nature force to reduce energy cost and, more importantly, to realize positive energy balance of algal biofuel production. This study aims to develop a horizontal photobioreactor, in which mixing can be provided with rocking movement driven by nature force. Results: Simple boxes were used as small-scale horizontal photobioreactors on a rocking platform for culture of alkalihalophilic Euhalothece sp. ZM001. There was no CO gas bubbling since 1.0 M NaHCO supplied sufficient inorganic carbon in it. Effect of culture depth, rocking cycle, and light intensity to algal biomass production, pH change, and DO accumulation were investigated in this system. Biomass concentration of 2.73 g/L was achieved in culture with 2.5 cm depth, and maximum productivity of 17.06 g/m/day was obtained in culture with 10 cm depth. k a in PBR with different culture depths and rocking cycles was measured, and it was from 0.57 to 33.49 h, showing great variation. To test this system at large scale, a plastic bag with a surface area of 1 m was placed on a rocking platform driven by water power, and it resulted in a biomass concentration of 1.88 g/L. Conclusion: These results proved feasibility of a novel photobioreactor system driven by nature force, as well as low cost of manufacturing, and easy scaling-up. [ABSTRACT FROM AUTHOR]