It comes after there were more deaths than births for the first time last year, prompting the government to take action.
Figures from 2015 showed that despite women on average wanting two or more children, those aged 18-49 had an average of 1.3, significantly below the EU average of 1.58.
The statistics mean Spain has one of the lowest birth-rates in the developed world.
The new ‘sex tsar’, Edelmira Barreira, will help draft a national strategy to tackle the demographic imbalances.
She has been appointed by Prime Minister Mariano Rajoy.
Spain’s education ministry said the declining birth-rate ‘aggravates other economic imbalances and generates important “impacts” in the Welfare State’.
Rafael Puyol of the Madrid IE Business School said people are too tired after a full day at work and blamed long working hours and late nights.
He said: “They do not help with making a family. Then a child arrives and it is even worse.”