<p>High-throughput experiments, unidirectional fluid replacement, real-time process monitoring, and simultaneous drug sensitivity and toxicity tests are hard to achieve on most existing tumor organoid chips. Here, we developed a gravity-driven organoid perfusion (GDOP) platform facilitating scalable throughput and supporting drug sensitivity and toxicity assessment on organoids. The unidirectional perfusion capability and optimized operational parameters of the GDOP chip were validated through fluid dynamics simulations. Using this platform, we successfully established uniform on-chip triple-negative breast cancer (TNBC) organoids, with endpoint detection results aligning closely with clinical diagnosis. Throughout the drug treatment process, we monitored and then analyzed the morphological and grayscale changes of the organoids. The sensitivity and toxicity tests revealed the optimal concentration range for the 3 chemotherapeutic drugs. In addition, on-chip brain organoids were established, which lays a feasible foundation for future drug toxicity tests of complex organoids. The GDOP platform, combined with its integrated evaluation method, provides a powerful and reliable approach for advancing organoid-based researches.</p>