This proceedings book contains selected and expanded contributions presented at the 6th International Symposium on Plasma and Energy Conversion (iSPEC 2025), held in Hong Kong SAR, China, on December 3–6, 2025. As the world continues to grapple with the pressing challenges of climate change and sustainable energy, iSPEC2025 aims to serve as a global platform for exploring cutting-edge advancements and innovative solutions in plasma and energy conversion. This symposium addresses the critical role of these technologies in achieving international carbon reduction goals and fostering a sustainable future. iSPEC2025 gathers leading scientists, researchers, and industry experts from around the globe to share their latest research findings, technological breakthroughs, and visionary ideas. Fields covered in this symposium include:• Renewable energy-driven plasma systems. • Fundamental processes, diagnostics, and simulations in plasmas. • Plasma-surface and plasma-interface interactions. • Synthesis and modification of catalytic and energy-storage materials via plasma techniques. • Plasma-enhanced catalytic processes: heterogeneous catalysis, photocatalysis, electrocatalysis, etc. • Plasma-assisted H2 energy technologies: production, hydrogenation, fuel reforming, etc. • Plasma-driven carbon cycle processes: methane activation, CO2 conversion and utilization, etc. • Plasma-enabled N2 fixation: NH3 synthesis, N2 oxidation, H2O activation, etc. • Conversion and utilization of biomass, plastics, and waste through plasma technologies. • Integration of plasma processes in micro-chemical engineering. • Plasma-enabled clean combustion technologies. • Emerging plasma-enabled energy conversion technologies. • Biomedical applications and effects of plasma. • High-voltage discharge testing. • Mechanisms and dynamics of electrical breakdown in insulating materials. • Pulsed power technology innovations and applications in plasma science. These proceedings are valuable references for researchers and students engaged in studies in all fields related to plasma and energy conversion.