Continuous monitoring of physiological activities within the internal regions of three-dimensional (3D) organoids holds significant promise for advancing organoid-based research. However, conventional methods are constrained to capturing signals from the peripheral surfaces of organoids, limiting insights into internal dynamics. Here, we present a soft 3D bioelectrode platform for continuous intraorganoid signal monitoring. These bioelectrodes, formed via 3D printing of liquid metal, are designed with customizable geometric parameters, including height and diameter, to adapt to various organoid structures. The tissue-comparable softness of the electrodes minimizes damage to cardiac organoids, ensuring a stable interface for reliable signal recording even under dynamic deformations caused by rhythmic contractions or displacements in aqueous environments. The array configuration enables simultaneous electrocardiogram (ECG) recordings from 32 organoids. Demonstrating real-time monitoring of drug-induced ECG responses, this scalable platform highlights its potential for high-throughput drug screening.