This study investigated the survival and catalytic potential of a single species Pseudomonas taiwanensis VLB120ΔC biofilm for the conversion of styrene to (S)-styrene oxide in a multiphasic capillary microreactor containing the highly toxic substrate styrene as a pure phase. The catalytic biofilm was cultivated under high fluidic stress in a continuous three-phase segmented flow system comprising aqueous medium, air, and styrene. This concept required an adaptation period of 7 days, during which P. taiwanensis VLB120?C developed a biofilm exhibiting a remarkable cellular integrity with nearly 70% intact cells. In a three-phase segmented flow biofilm microreactor, an average specific styrene epoxidation rate of 10 g/Ltube/day was achieved continuously for a period of 20 days without any clogging problems. Overall, this note highlights the robustness of biofilms as a promising biocatalyst format for the conversion/synthesis of toxic organic chemicals and the applicability of multiphasic capillary microreactors for biofilm based catalysis.