The summer signing notched his second goal, and first in the Premier League, but the newly promoted outfit held on to secure a valuable point against the Gunners.
Leicester's record signing headed home in the 22nd minute to immediately cancel out Alexis Sanchez's first league goal for Arsenal since joining from Barcelona.
|VIEW FROM KING POWER STADIUM
|By Peter Saunton
Another outing to emphasise Arsenal's drastic need for flesh blood up front.
They have been linked with Carlos Bacca, an international forward of some repute, and he cannot come quick enough as Yaya Sanogo struggles in the absence of Olivier Giroud.
Arsenal have an over-abundance of playmakers and not anybody to take the chances they create.
For Leicester, they will be pleased with this showing a point against Arsenal is welcome in any context and yet they might feel they could have won it. It was they who created the better chances besides the goal.
Arsenal headed into the game desperate to cap a good week, having qualified for the UEFA Champions League group phase for the 17th successive season on Wednesday.
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Yet an inspired Ulloa proved a handful and, with Leicester also defending doggedly, Arsene Wenger's men had to settle for a share of the spoils.
Arsenal has now collected a win and two draws from the opening three league fixtures of 2014-15, with Leicester taking two points from the same number of games.
The home side began confidently, Ritchie De Laet sending in a teasing cross for Ulloa - whose attempt to control the ball flew straight to Wojciech Szczesny.
Arsenal found itself briefly depleted when Laurent Koscielny was forced to go to the dressing room for stitches to a head wound following a nasty collision with Jeffrey Schlupp.
Leicester almost made full use of the one-man advantage when Riyad Mahrez hit just wide following a fine one-two with Ulloa.
Soon after Koscielny returned to the field, Arsenal took the lead through Sanchez after 20 minutes.
Santi Cazorla's wonderful lobbed pass freed Yaya Sanogo and, after the striker's woeful effort was blocked by Kasper Schmeichel, the Chilean was left with a simple finish.
Yet Leicester found an immediate riposte through Ulloa, who met Schlupp's stunning cross with a powerful header that gave Szczesny no chance.
Koscielny, still suffering from the effects of his earlier injury, was at fault for the goal and it came as no surprise when Calum Chambers replaced him.
Arsenal continued to dominate possession after halftime, but was fortunate not fall behind when Ulloa chipped into the side-netting after brilliantly turning Chambers.
The visiting side fashioned a couple of chances of its own almost immediately after, Aaron Ramsey heading tamely at Schmeichel before Sanogo hit straight at the goalkeeper when clean through.
Leicester, though, was always on hand to fire warning shots of its own, David Nugent seeing a goal-bound effort blocked following good work from the outstanding Ulloa.
The game entered something of a lull thereafter as neat Arsenal football failed to bring chances.
That impasse ended when substitute Jamie Vardy came agonizingly close to grabbing a second Leicester goal, Szczesny producing a fine reactionary save.
Alexis Sanchez opened the scoring after 20 minutes only for Leonardo Ulloa to equalize less than two minutes later.