Type 1 ryanodine receptor (RyR1) is a Ca²⁺-release channel on the sarcoplasmic reticulum (SR) of skeletal muscle. Genetic mutations in RyR1 cause various muscle diseases including malignant hyperthermia (MH). The main underlying mechanism of the pathogenesis is overactivation of Ca²⁺ release from the SR, which is brought by gain-of-function of the RyR1 channel. Therefore, inhibition of RyR1 is expected to be a promising treatment for the diseases. We have recently developed an efficient high-throughput screening (HTS) platform for RyR1 inhibitors and identified three novel compounds from a library of well-characterized drugs (Murayama et al., Mol Pharmacol, 94: 722-730, 2018). However, only oxolinic acid was found to be selective for RyR1 among the three compounds. To explore another RyR1-selective inhibitor, we performed further HTS using a library of larger numbers of compounds. Using Ca²⁺ measurements in the endoplasmic reticulum, we successfully obtained 8 compounds that inhibit RyR1 and 4 compounds were RyR1-selective. [³H]Ryanodine binding assay revealed that they inhibit RyR1 without changing Ca²⁺ dependence. They were structurally different from each other and from known RyR1 inhibitors. Potential binding sites were searched using chimeric channels of RyR1 and RyR2. These compounds will be potential candidates for a novel RyR1-selective inhibitor.