In Croatia, the pope railed against practices such abortion, cohabitation as a "substitute for marriage," and artificial birth control.
Pope Benedict warned on Sunday that the traditional family in Europe was "disintegrating" under the weight of secularisation and called for laws to help couples cope with the costs of having and educating children.
On the second day of his trip to Croatia, a bastion of Roman Catholicism in the Balkans, the pope said an open-air mass for hundreds of thousands of people and hammered home one of the major themes of his papacy.
"Unfortunately, we are forced to acknowledge the spread of a secularisation which leads to the exclusion of God from life and the increasing disintegration of the family, especially in Europe," he said in his sermon on the edge of the capital.
The 84-year-old Benedict's sermon was the latest in a series of salvos against what the Church sees as growing anti-Catholicism and "Christianophobia" in Europe.
Speaking on the day Croatia, whose population of 4.4 million people is 90 percent Catholic, celebrates its "Family Day", he railed against practices such abortion, cohabitation as a "substitute for marriage", and artificial birth control.
The pope urged Catholic families throughout Europe not to give in to a creeping "secularised mentality" and called for "legislation which supports families in the task of giving birth to children and educating them".
The sermon reflected the Vatican's belief that the Catholic Church in Europe is under assault by some national governments and European institutions over issues such as gay marriage, abortion, religious education and the use of Christian religious symbols in public places.
Last year the Vatican criticised plans to propose legislation in Britain, known as the Equality Bill, that could force churches to hire homosexuals or transsexuals.
The Vatican was also at the forefront of a campaign that overturned a ruling by the continent's top human rights court that would have banned crucifixes in schools in Italy.
At the start of the trip on Saturday, the pope criticised the European Union, saying its bureaucracy is overly centralised and sometimes neglected historical differences and national cultures.
The Vatican strongly supports Croatia's bid to become an EU member, which it is expected to achieve in 2013. This would put another overwhelmingly Catholic country in the bloc.
Benedict's trip to Zagreb is intended to encourage the local Church, 20 years after independence and 16 years after the end of the Balkan wars.
Later on Sunday he will pray at the tomb of Cardinal Alojzije Stepinac, who was accused of collaborating with the Nazi-allied rulers during World War II. The communists sentenced him to 16 years in confinement after the war.
The late Pope John Paul beatified Stepinac in 1998, putting him one step away from sainthood.
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