Burglars forced a downstairs window to get inside the house near Kilmeston village.
They were disturbed when the owner returned and drove off with several items of jewellery, antiques including an engagement ring, a set of four naval paintings, a carriage clock and a silver dish.
Hampshire police said at least two suspects were involved and one was described as early to mid-20s, athletic, around 6ft tall and wearing a grey, baggy top.
Police investigator Peter Davies said: ''This is a burglary on a large country house where several items of high sentimental and monetary value have been taken.
''There is a good chance the suspects were in the area of the house some time prior to the incident.
''We would appeal to anyone who may have been in the area at the time of the burglary to contact us if they saw anyone acting suspiciously or saw any vehicles acting in a suspicious manner.
''We would advise owners of large country residences to always ensure their properties are secure and to review their security as a matter of course."
Anyone with information should contact Winchester police station on 0845 045 45 45 or Crimestoppers anonymously on 0800 555 111.
Art Hostage comments:
Art Hostage was once asked if he was a Naval man ?
Art Hostage replied, "No, more of leg man !!"
Well, it did say a set of four Naval paintings were stolen.