Ulster scored five tries - all in the second half - from Robbie Diack, Andrew Trimble, Nick Williams, Neil McComb and a penalty try. Ruan Pienaar kicked all four conversions and two penalties on his 50th appearance.
The Scarlets, who got tries through Josh Turnbull and Scott Williams, will be bitterly disappointed at this showing which saw Aled Thomas - who scored a penalty and a conversion - again yellow carded late on.
The result, Ulster's 12th victory in 13 league games, means they now head into two weeks of European action - where they are Pool Four leaders - in good shape. However, the Scarlets have now fallen to their fifth defeat in six games - and that run looks likely to worsen as the bottom side in Pool Five fulfil their European pool fixtures over the next fortnight.