Phil Gormley said he was co-operating fully with the inquiry by the Police Investigations and Review Commissioner (Pirc).
In a statement released last night, Mr Gormley said: “I can confirm that today I was informed by the PIRC that I am the subject of a conduct investigation.
“I am cooperating fully with the PIRC and will provide all necessary assistance to bring this matter to a timely and satisfactory conclusion. In fairness to others who may be involved, it is not appropriate for me to comment further at this time.
“I would like to stress that I remain focussed on leading Police Scotland, ensuring that we continue to serve and protect the people of this country.”
The Pirc defines gross misconduct as “a breach of the Standards of Professional Behaviour, as detailed in Schedule 1 of the 2013 Regulations, which is so serious that dismissal may be justified”.
The standards cover: honesty and integrity; authority, respect and courtesy; equality and diversity; use of force; orders and instructions; duties and responsibilities; confidentiality; fitness for duty; and discreditable conduct and challenging and reporting improper conduct.
A Scottish Police Authority (SPA) spokesman said: “If an allegation relating to the conduct of a senior officer of ACC rank or above is made, the SPA has the responsibility for receiving and assessing that allegation in line with The Police Service of Scotland (Senior Officers) (Conduct) Regulations 2013.
“If the SPA decides that a misconduct allegation is to be investigated, it must refer the allegation to the independent Police Investigations and Review Commissioner (PIRC).”