The　flow　channel　configuration　affects　microbial　inactivation　efficiency　in　water　because　it　considerably　influences　hydrodynamics　and　ultraviolet　(UV)　light　distribution.　The　ratio　of　channel　length　to　breadth　(alpha)　and　the　ratio　of　channel　width　to　depth　(beta)　of　a　serpentine　flow　channel　on　Escherichia　coli　inactivation　efficiency　were　investigated.　Simulations　revealed　that　when　alpha　was　1.0,　the　flow　channel　had　a　uniform　velocity　distribution　and　performed　the　longest　microbial　residence　time.　Furthermore,　biodosimetry　tests　indicated　that　when　beta　was　1.0,　the　reactor　resulted　in　a　maximum　inactivation　efficiency　of　3.7　log　when　the　distance　between　the　UV　LEDs　and　the　water　was　11.5　mm.　The　optimal　aspect　ratio　beta　led　to　the　ideal　balance　between　microbial　residence　time　and　UV　irradiance,　resulting　in　the　highest　UV　fluence　(10.6　mJ/cm2)　for　the　bacteria.　The　inactivation　efficiency　observed　at　the　aforementioned　aspect　ratio　was　approximately　48%　higher　than　that　observed　at　an　aspect　ratio　of　2.56.　Additionally,　decreasing　the　distance　between　the　UV　LEDs　and　the　water　from　11.5　to　3.5　mm　enhanced　the　inactivation　efficiency　at　all　aspect　ratios　because　of　the　considerable　increase　in　UV　irradiance　in　the　water.