A 26-year-old Algerian is charged with attempted sexual assault and theft.
He is accused of being part of a group of 10 men who surrounded and groped a woman in the main railway station in the early hours of New Year’s Day.
The large-scale sexual assaults and robberies by men of North African and Arab appearance shocked Germany.
More than 1,000 criminal complaints were filed, hundreds of them alleging sexual assault, after women reported being surrounded by groups of men in and around Cologne’s main station.
The 26-year-old whose trial begins on Friday denies the charges against him.
According to prosecutors, after the group of men surrounded the woman victim, some of them proceeded to touch her on the buttocks and other areas “in a sexually motivated way”, for two to three minutes.
The defendant allegedly used this opportunity to steal her mobile phone.
On trial with him is a 23-year-old Algerian – his brother, according to German news agency DPA – who is accused of stealing another woman’s mobile phone as she was surrounded.
Nine men have already been convicted of theft and similar charges in relation to the events of New Year’s Eve, state prosecutors say.