Three quarters of the 307 dossiers opened were in northern Flanders, the staunchly Catholic Dutch-speaking and larger half of Belgium.
The great majority of complainants were mature adults, having waited before coming forward after the Church fell into scandal over recent years and with compensation now an issue.
Forty-six of the cases raised last year have gone forward for mediation, officials behind the abuse census said.
After similar scandals in the United States, Ireland and Germany, Belgium was rocked in April 2010 with revelations that the then bishop of Bruges, Roger Vangheluwe, had abused a nephew for 13 years.
Vangheluwe's subsequent decision to quit opened a floodgate of allegations, with one report revealing almost 500 cases of abuse in Catholic institutions since the 1950s, including 13 known suicides by victims.
In September 2011 some 70 alleged victims filed joint legal action against the Belgian Church and the Holy See, the first such class action suit in Belgium and the first such suit involving the Vatican in Europe.