The record for the widest winning margin in an international rugby match is held jointly by Argentina and Japan; interesting the record was set by Argentina on May 1, 2002 and equalled by Japan just over two months later.
In their match, against Paraguay, at the Mendoza Rugby Club in western Argentina, Los Pumas ran up a score of 152 points, including 24 tries, without reply; left wing Facundo Soler, right wing Jose Nunez Piossek and lock Pedro Sporleder all scored four tries apiece. Not to be outdone, in their match, against Chinese Taipai, at the Prince Chichibu Memorial Stadium in Tokyo, the Cherry Blossoms scored 155 points, including 23 tries, with just a solitary penalty in reply; left wing Daisuke Ohata, who later became the leading tryscorer in international rugby, scored eight tries.
Coincidentally, Japan were on the receiving end when New Zealand recorded the widest winning margin in the history of the Rugby World Cup, in South Africa in 1995; the All Blacks ran in a record 21 tries en route to a 145-17 victory.
For the record, in club rugby, the widest winning margin was achieved, under peculiar circumstances, in a match between Royal Kituro and Soignies in the top division of the Belgian league in 2015. After the referee was delayed, by over an hour, the most of the Soignies players departed, along with their coach, assuming the match had been cancelled. However, the match did go ahead and, in protest, the remaining Soignies players allowed the opposition to score, unhindered, throughout the match. Royal Kituro eventually scored 356 points, including 56 tries, against a lone drop goal, to win by a margin of 353 points.