PATIENTS' lives will be put at risk if the right nurses with the necessary skills are not in charge of their care, experts there warned.
They also called on the National Assembly to pass a law requiring the provincial government to publish its plans for future nursing numbers.
At the moment there is widespread concern about workforce plannings.
Senior health experts told the Western Mail, leading daily, that too often plans for how many new nurses Wales needed to train were based not on health need, but on how many nurses were trained the previous year and how many the country can afford.
Tina Donnelly, director of RCN Wales said, "The nursing workforce forms the largest part of the NHS and nurses also play a vital part in delivering healthcare in the independent sector.
"We must get the numbers of nurses and healthcare assistants required right and ensure the skill-mix of those who are qualified and those who are trained and working alongside healthcare support workers is at the optimum safe level.
"In recent years we have begun to focus our attention on delivering care as close as possible to the patient and often within their own homes. The nursing workforce we require must have the right balance of skills to do this effectively and safely."
In evidence submitted to the Assembly's health, wellbeing and local government committee inquiry into workforce planning arrangements, the RCN quoted research work by Professor Anne Marie Rafferty, professor of nursing policy and Dean of the Florence Nightingale School of Nursing and Midwifery at Kings College London.
She surveyed nearly 4,000 nurses and looked at 118,752 patient episodes of care in 30 hospital trusts in England.
The research found wards with a lower nurse to patient ratio had a 26% higher patient mortality rate.
But those hospitals where the number of nurses per patient is greater had significantly lower surgical mortality rates.
Prof Rafferty said that had there been more nurses on the wards, 246 lives could have been saved.
The RCN believes a higher number of registered nurses and a higher proportion of registered nurses in the nursing workforce helps reduce patient mortality, infection rates, patient falls, the incidence of pressure sores and mistakes administering medication.
Ms Donnelly added, "The current way in which the Welsh Assembly Government commissions nurse training is not sufficiently robust to guarantee professional or public confidence.
"A published workforce plan, required by law, will ensure that this is put right.
"The nation deserves to know that the number of nurses we have and the skills they possess is appropriate to the needs of 21st century healthcare."
A spokesman for the Welsh Assembly Government said, "A new integrated workforce planning process is being implemented within the NHS in Wales and has been developed in consultation with a stakeholder group of which RCN is a member.
"Previously, workforce plans were based on what NHS trusts told us they required over the next five years. We have changed this to take into account a range of issues which integrate service planning, financial planning and workforce planning."