The demonstration in the capital Warsaw came after the Prime Minister Beata Szydlo suggested she was in favour of a Catholic Church proposal to outlaw terminations.
She stood for election on a platform to "restore Catholic values" to the nation.
Prime Minister Beata Szydlo
Abortion is currently illegal in Poland in most cases but there are exceptions if the pregnancy poses a threat to the woman's health or life, if it results from a crime like incest or rape or if the foetus is damaged.
Protesters say a total ban would lead to women dying or it would force them to travel to other countries for abortions. In Warsaw, they strung up coat hangers, a symbol of primitive underground abortions.
The rallies in Warsaw and other cities were held under the slogan "No to the torture of women".
The current abortion law dates to 1993 and was a compromise between the country's liberal and Catholic circles.
Priests across Poland read out a letter from bishops in churches calling for politicians to initiate legislation that would impose the total ban on abortion. The letter argued there can be no compromise on the matter, citing the Biblical precept "Thou shalt not kill".
The ruling Law and Justice party has a majority in parliament and would be in a position to change the abortion law if all of its lawmakers support that change. It is not yet clear if most would follow party leader Mr Kaczynski in supporting the ban.