The privately owned, Cardiff-based contractor saw a slowdown despite an increase in turnover from £32.2m to £46.9m in the same period.
It had enjoyed a 130% hike in profit in 1997 and had promised to pursue repeat business and larger projects.
It blamed this year’s drop in profit on the current industry climate.
“The drop in margins reflects the increasingly competitive market in the construction industry today,” a Cowlin statement said. “Efforts are being made, with some success, to maintain turnover and profitability in the current year to a similar level to that of 1998.”