Former Glamorgan all-rounder Jim Allenby led the way with 131 not out for Somerset on the first day of a three-day friendly in Cardiff.
The visitors declared on 323 for seven with Allenby striking 21 fours and two sixes, after losing half their wickets for just 73.
Graham Wagg with two for 22 in ten overs was the most successful of Glamorgan's eight bowlers.
Glamorgan finished day one on 75 for no wicket.
Allenby, who spent six seasons at Glamorgan, received useful support from Ryan Davies (40), Lewis Gregory (34) and Craig Overton (42 not out) after the Glamorgan seamers dominated the first session.
Wagg dismissed former England opener Marcus Trescothick without scoring while ex-Australia batsman Chris Rogers fell to David Lloyd for 23.
James Kettleborough (30 not out) and Mark Wallace (45 not out) batted out 23 overs before the close.
Somerset start their Championship campaign away to Durham on 10 April in division one while Glamorgan have a first-class friendly against Cardiff MCCU on 11 April before facing Leicestershire the following week.
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