The woman crossed Sydney Road after noticing the man behind her, but he continued to follow her.
"As she crossed the road, the man sexually assaulted her before walking away on Merri Street," police allege in a statement.
The man is perceived to be aged in his mid-20s, approximately 170cm tall with light brown crew-cut hair and a receding hairline.
Police have appealed for anyone with information to come forward after a woman was allegedly sexually assaulted on a Melbourne street.(Victoria Police)
He was wearing a red Nike hooded top with the slogan 'Just Do It' written on the front.