Humberside Police said the officers found suspected heroin and crack cocaine as well as cash when they detained the 21-year-old man.
A spokesman said: "A 21-year-old man has been arrested on suspicion of possessing a class A drug with intent to supply after being spotted by plain clothes officers while he was allegedly dealing drugs.
"The arrest was made today on a pathway running between Great Thornton Street and Whitebeam Close in Hull.
"Eleven wraps of what's thought to be heroin, and twenty four wraps of suspected crack cocaine which were hidden in a cigarette packet were seized."
Police said the drugs had an estimated value of £800 and hundreds of pounds in cash was also seized.