AUCKLAND, Jan 25 - Commissioned by teachers' union the New Zealand Educational Institute, the study found around 72 per cent of principals and their deputies worked more than 51 hours per week with 25 per cent working more than 61 hours.
Even during term breaks, half worked more than 25 hours a week.
NZEI president Lynda Stuart says this was compounded by a lack of professional support from the Ministry of Education or school board trustees, who employ the principals.
"This situation is not sustainable and places significant health risks on the people leading our schools," she said.
"It's now a major health and safety risk that the government must address."
In addition to the workloads, the school heads reported being most stressed about their inability to focus on teaching programmes as well as the extra red tape associated with new government initiatives.
This led to work-family conflict among principals and deputies that was 2.2 times the rate of the general population and burnout 1.7 times the general population, the study found.
Stuart said the Ministry of Education needed to act to reduce principal's workloads and supported the study's recommendations that school heads be given opportunities to access professional support networks and mentoring.
Despite the stresses, the study also found the principals and deputies were generally positive abut their jobs and reported a higher job satisfaction than the general population.
The study undertaken last year by Australian Catholic University surveyed 398 primary principals, or 20 per cent of New Zealand's total, and 145 deputy and assistant principals.