Blair's new book, "A Journey," is a best-seller, but it has angered opponents of his policies, especially the 2003 invasion of Iraq.
About 200 demonstrators chanted that Blair had "blood on his hands" as the former prime minister arrived at a Dublin bookstore.
Shoes, eggs and other projectiles were thrown toward Blair as he emerged from a car, but did not hit him. A flip-flop could be seen lying on the roof of a BMW in Blair's motorcade.
Security was tight, with book buyers - who appeared to outnumber the protesters by about two to one - told to hand over bags and mobile phones before entering Eason's bookstore on O'Connell Street, Dublin's main shopping thoroughfare.
There were scuffles between police and demonstrators when some tried to force their way through the security cordon. Two protesters were bundled into the back of a security van. Several demonstrators, including one wheelchair user, laid themselves in the van's path, and riot police were brought in to remove them.
Police said four men were arrested and charged with public order offenses.
Blair spent about two hours in the store before emerging to more shouts, boos and hurled eggs. He was quickly driven away, as a police helicopter circled overhead.
"Blair took the world to war in Iraq and Afghanistan on the basis of lies," protester Donal MacFhearraigh said. He said Blair should be indicted as a war criminal.
Another protester, 24-year-old Kate O'Sullivan, said she was taken away by security guards after approaching Blair in the store and trying to perform a citizen's arrest.
Confrontation erupted again once Blair had left, as police stopped demonstrators from entering the bookstore. Many of the demonstrators then marched to the police station where those arrested were being held to continue their protest there.
Despite the protests, Blair is popular with many in Ireland for his role in forging the 1998 Good Friday peace accord in Northern Ireland, and several hundred people lined up in the rain to have their copies of "A Journey" autographed.
"I appreciate what he did for Irish politics, particularly along the border. That's why I've come," retiree Maureen Hedderman told the Press Association news agency.
Released this week, "A Journey" is Amazon's best-selling title in Britain, and has climbed into the top 10 on the online retailer's U.S. chart.
Blair was paid a 4 million pound ($7 million) advance for the memoir, which mounts a strong defense of his policies during his years as prime minister from 1997 to 2007, including the invasion of Iraq.
Blair says in the book that he is not sorry for his decision to enter the U.S.-led war, although he has wept for its victims. He is donating all proceeds from the book to a charity for wounded troops.
In an interview aired Saturday, Blair rejected claims that the invasions of Iraq and Afghanistan had increased Muslim radicalization, saying "wicked and backward-looking" radical Islam is the greatest threat to global security.
Blair told the BBC World Service "the biggest threat in international security is this broader radicalized movement, because I think it is rather similar to revolutionary communism."
He said al-Qaida-linked extremism was "loosely a global ideological movement, but Iran is a state sponsor of it."