Police allege the woman stabbed a 74-year-old man at a business on Puckle Street in Moonee Ponds about 11am today.
The armed woman, described as being in her 30s or 40s, then fled the scene towards Hall Street, police say.
The man from Avondale Heights was taken to Royal Melbourne Hospital with non-life-threatening injuries.
Police are searching for the alleged offender who was last seen wearing a black t-shirt and black pants and is approximately 160cm tall.
Anyone who witnessed the incident is urged to contact Crime Stoppers.
