Japan featured at the Confederations Cup last June after winning the 2011 Asian Cup but they failed to win a game in Brazil.
The Asian champions were beaten by host nation Brazil (3-0), Italy (4-3) and Mexico (2-1).
Japan are now back in Brazil a year later and Zaccheroni said he believes his team have matured on the eve of their Group C clash against Ivory Coast.
"I don't like to make proclamations, I'm a man who has his beliefs," said the Italian. "I believe the team has improved.
"In the last important competition, the Confederations Cup, we failed the maturity test.
"Since then, 12 months have gone, in the meantime the team have gained experience and me too. I'm curious to see in this test how much we've improved.
"For sure, we've improved, now let's see the first few games and then I can be more precise."
While Japan have improved since the Confederations Cup, they are still conceding too many goals as defence continues to be cause for concern for Zaccheroni.
Japan shipped four goals in their past two pre-World Cup friendlies, with three of those coming against Zambia.
And defender Maya Yoshida has called for concentration as Japan prepare to come up against the likes of Didier Drogba, Wilfried Bony, Gervinho and Salomon Kalou.
We all know that we've given up too many goals (lately)," said Yoshida, who plays for Premier League outfit Southampton.
"As well as in set-plays, we often get beaten even when we have enough people, so what we need to do are, we need to focus in set-plays.
"We want to get the opponents away from the goal as much as possible, not stepping back too much."
