The firm said market conditions "continued to be challenging" but that they anticipate a return to growth in 2014.
Northstone showed a pre-tax profit of ??6m on turnover of ??239m, compared to 2012 when profit of ??8m was achieved on a ??299m turnover.
Its best-known trading business is the Farrans construction firm.
It also sells quarry products and ground access systems for the utility industries.
The fall in group turnover in 2012 was all attributable to its building/civil engineering division where turnover fell from ??226m to ??153m.
The company's workforce fell from 992 to 968 over the year and the accounts show redundancy costs of ??358,000.
During the year, the firm bought the Cemex (NI) cement business for an undisclosed sum.
Northstone is ultimately owned by CRH plc, the Dublin-based building materials group which is worth around ??10bn.

The Pirates of the Caribbean star will play the title role in Therese Raquin, based on Emile Zola's 1867 classic.
Described as "a tale of love, lust, betrayal, and guilt," the play will cast her as a young woman trapped in a loveless marriage who has an affair with one of her husband's friends.
The Roundabout Theatre Company show opens in October 2015 in New York.
Knightley, who turns 30 next year, previously trod the boards in London in The Misanthrope and The Children's Hour.
The actress has two films out next month in the UK - World War Two drama The Imitation Game and US comedy Say When.
Therese Raquin has been staged and filmed many times, most recently as the film In Secret starring Elizabeth Olsen.
The new version is by British playwright Helen Edmundson, who previously adapted the Tolstoy novels Anna Karenina and War and Peace for the stage.
Knightley appeared in a 2012 film of Anna Karenina and has also appeared in film adaptations of Pride and Prejudice and Ian McEwan's Atonement.
Therese Raquin begins previews on 1 October and has its opening night on 29 October at a Broadway theatre yet to be announced.
Earlier this year Knightley revealed she had hoped to take The Children's Hour to Broadway but could not work out the scheduling with co-star Elisabeth Moss.
"We tried to make it happen, but our scheduling didn't work out," she told The Advocate. "It was a real shame, because it would be great doing it on Broadway."
Northstone, one of Northern Ireland largest construction groups, reported reduced turnover and profits in 2013.
[NEXT_CONCEPT]
British actress Keira Knightley is to make her Broadway debut next year in a stage version of a famous French novel.