Abstract: Helical cruciform nuclear fuel offers short heat transfer paths, large specific surface area, and strong self-mixing and self-positioning capabilities, making it a promising candidate for advanced reactors. However, the phase distribution of gas-liquid two-phase flow in such complex twisted rod bundle channels remains poorly understood. This study aims to experimentally investigate local phase distribution characteristics including void fraction, bubble velocity, and interfacial area concentration in a 4×4 helical cruciform rod bundle channel under bubbly flow conditions. A double-sensor conductivity probe was employed. The probe consisted of two stainless steel sensors (0.12 mm diameter) insulated with polytetrafluoroethylene and housed in a brass tube (1.6 mm outer diameter), with an axial spacing of 1.4 mm. Measurements were taken in a vertical test section at 208.4 hydraulic diameters downstream of the inlet. Radial positioning was controlled by a motor-driven system (±0.02 mm repeatability), covering 24 points at 1 mm intervals. Bubbles (1-3 mm diameter) were generated by a gas-liquid mixer with four porous metal tubes. Nine test conditions were investigated: gas-phase superficial velocities of 0.015-0.036 m/s and liquid-phase superficial velocities of 0.5-1.5 m/s, all within the bubbly regime. Signal sampling was performed at 50 kHz for 60 s per point. Calibration via high-speed visualization gave relative uncertainties of ±6.0% for void fraction and ±9.5% for gas velocity and interfacial area concentration. The results show that bubble distribution is jointly regulated by transverse flow, swirling flow, lift force, and bubble spiral trajectory. In gap regions between adjacent rods, strong transverse and swirling flows promote coalescence of Group-1 bubbles into larger Group-1 or Group-2 bubbles, significantly increasing void fraction and interfacial area concentration at gap centers. Lift force drives bubbles toward trough regions, while transverse flow pushes small bubbles toward blade tips, producing a distinct concave distribution profile between adjacent rods. At a low liquid-phase velocity of 0.5 m/s, Group-2 bubbles contribute up to 3.5% and 6.3% void fraction in two types of gaps, respectively. When liquid-phase velocity increases to 1.5 m/s, enhanced turbulence suppresses coalescence and reduces Group-2 bubbles. Thus, the phase distribution becomes dominated by Group-1 bubbles and is governed primarily by transverse flow, lift, swirling, and bubble spiral motion. This study provides a detailed experimental database of local two-phase flow parameters in a helical cruciform rod bundle channel, reveals complex phase distribution mechanisms, and offers an experimental basis for developing local parameter prediction models as well as for reactor thermal-hydraulic design and safety analysis.