Unofficial sources have reported that the 50-page document, entitled "God is love" will be published Friday at a news conference, the Italian Ansa news agency said.
But there has been no indication from the Vatican press service to that effect.
Ansa said that based on what "it had been able to learn" the document fell into two parts.
It opens with a quotation from the first Epistle of St. John the Apostle:
"God is charity and he that abideth in charity abideth in God and God in him."
In more recent translations the word "charity" is replaced by "love."
In the encyclical the pope underlines the link between love and charitable action, saying it will remain esssential "even in a more just society."
He warns against any attempt to separate two aspects of love: "agape", a Greek word denoting love based on kindness and fellowship, and "eros", another Greek word denoting love arising from passion, because without "agape" "eros" can finish by "being reduced to simple sex" and becomes "merchandise".
A senior Vatican official said last month that the encyclical, on which the pontiff had been working since the summer, would be published in January.
Translation problems accounted for the delay in publication, according to several sources.
The pope wrote in his native German, which then had to be translated into Latin, the theological language of the Roman Catholic Church.
The main sections then had to be put into several languages ahead of worldwide publication.
The mass circulation Famiglia Cristiana has told its readers it will publish a million copies of its January 25 edition containing the document.