The monarch butterfly (Danaus plexippus) is emerging as a model organism to study the mechanisms of circadian clocks and animal navigation, and the genetic underpinnings of long-distance migration (1). MonarchBase was developed as a public database for readily accessing the monarch genome and related biological processes (2). MonarchBase is an open-access, web-available portal that utilizes a variety of retrieving methods to access data conveniently and for integrating biological interpretations. The initial assembly of the monarch genome was released in 2011, and the biological interpretation of the genome focused on the butterfly’s migration biology (3). With the recent accomplishment of assembly improvement, MonarchBase provides access to an updated version of genome assembly (v3) upon which all data integration is based. Genome browser is available for browsing detailed annotations along the reference genome. Gene pages were designed with an integrated representation of the functional annotations, alternative gene models, expression profiles, and assignments to InterPro domains, Gene Ontology (GO) terms, and KEGG pathways. MonarchBase invites colleagues to submit manual curations and additional datasets for integration.