MicroRNAs (miRNAs) are endogenous non-coding small RNAs that function as diverse gene regulators at the post-transcriptional level. Over the past two decades, intense research efforts on miRNA identification, function and evolution have raised the demand for miRNA databases. We constructed a knowledge-based database called Plant miRNA Encyclopedia (PmiREN, https://pmiren.com/ ) in 2019 and continued to update it. PmiREN is based on the uniform processing of sequenced small RNA libraries using miRDeep-P2. It currently contains 38,186 high confidence miRNA loci from 179 plant species and incorporates multiple tools for data mining and data-driven research. Here, we summarize the usage of PmiREN, aiming to serve the entire research community of plant miRNAs.