"Worcestershire had a good run in the T20 last season in reaching the quarter-finals and I hope I can play my part in helping them to enjoy another successful tournament."
The left-armer has taken over the T20 overseas slot from big-hitting international teammate Colin Munro, and Worcestershire Director Of Cricket Steve Rhodes is delighted to have him on board.
"To have an overseas player with three strings to his bow will be a huge bonus to our T20 Blast ambitions," says Rhodes.
"He is a genuine left arm spinner so he will give our bowling terrific balance and his athletic fielding will add to an already good fielding squad."
Santner has played two T20 internationals for New Zealand, and shone with the ball at the domestic level, twice conceding just nine from his four over spell and holding a sterling career economy rate of 6.2.
Santner and Henry will join Munro and Mitchell McClenaghan in having played for the club in recent seasons, while Glenn Turner is an all-time great - having scored the third-most first-class runs in Worcestershire history.
Last year's T20 competition had seven New Zealanders competing - Munro, Jeetan Patel, Brendon McCullum, Luke Ronchi, James Franklin, Grant Elliott and Jesse Ryder.
McCullum recorded the highest score, bashing an unbeaten 158 from 64 balls with 13 fours and 11 sixes.
