The double-lined mackerel (Grammatorcynus bilineatus), is a species of Spanish mackerel (tribe Scomberomorini) in the family Scombridae. This species is sometimes also called the scad mackerel (not be confused with the mackerel scad in the Carangidae family). This is unique among fish, as most only have one on each side of the body.
left|thumb|230x230px|Juvenile with a spotted pattern
Grammatorcynus bilineatus can reach a maximum length of about , with a common length of about and maximum weight of about .
This species is often confused with its sister species Grammatorcynus bicarinatus, the shark mackerel.