A Simple Thinking About Blood Type () is a South Korean four-panel webtoon by art teacher Park Dong-sun () under the art name "Real Crazy Man". The webtoon is themed around blood type personality classification and is serialized on Dong-sun's blog. The webtoon has been published in book form and has been adapted into an anime series.
A Simple Thinking About Blood Type was first serialized on Dong-sun's blog as a webtoon. Japanese publisher Times Culture later published the comic in book form as in 2013.
A short anime adaptation was made by Japanese production houses Assez Finaund Fabric and Feel in 2013, with a second season in January 2015. Zexcs co-produced a third season, which began airing in October 2015. A fourth season aired in 2016.
Each of the voice actors also represents their own blood type.