Thames Valley Police said the woman threw the chips at a 16-year-old boy and a 16-year-old girl before punching one of them ‘a number of times’ in the racially aggravated attack.
The pair were approached by the woman at about 5.45pm on Thursday last week on Oxford High Street.
The victims tried to take shelter in Hardy’s Sweet Shop to avoid the woman but she followed them into the shop and punched one of the teenagers in the face and the head.
Police said the woman made racist comments towards the pair and the boy received minor injuries, but did not require hospital treatment.
Police described the woman as white with a skinny build and shoulder length curly dark hair.
She is aged in her late 20s and was wearing a dark coloured vest top with dark bottoms.
She had a large tattoo on her upper right arm, and Asian symbols on her upper back. She was holding a number of shopping bags, the force added.
Investigating officer PC Robb Prout, from Cowley police station, said: “This was obviously a very upsetting and concerning incident for the victims.
“This incident took place at a busy time of the day, and there would have been a number of people inside the shop at the time who may have vital information regarding this incident.”
Contact police on 101 if you have any information that could help.