Bangladesh bowled out for 240 in final game of the series.
Seamer Dhammika Prasad claimed three wickets in his first match of the series as new-look Sri Lanka restricted Bangladesh to 240-8 in the third and final one-day international in Dhaka on Saturday.
New-ball partner Suranga Lakmal finished with two for 24 in 10 overs after Sri Lanka, enjoying an unassailable 2-0 lead in the series, won the toss and elected to field at the Sher-e-Bangla stadium.
Mominul Haque top-scored with a run-a-ball 60, while valuable contributions from Nasir Hossain (38), Naeem Islam (32) and skipper Mushfiqur Rahim (30) gave the hosts their highest score in the series.
Sri Lanka took the field without either of their three veterans, Mahela Jayawardene, Kumar Sangakkara and Tillakaratne Dilshan, for the first time in a one-dayer since 2000.
Jayawardene and Dilshan were nursing injuries, while Sangakkara was rested ahead of the five-nation Asia Cup which opens in Bangladesh on Tuesday.
The hosts missed premier all-rounder Shakib Al Hasan, who was handed a three-match ban for a lewd on-camera gesture during the second one-dayer on Thursday.
Sri Lanka won both the preceding Test and Twenty20 series.
First-innings scoreboard in the third and final one-day international between Bangladesh and Sri Lanka in Dhaka on Saturday:
Anamul Haque c Chandimal b Prasad 2
Shamsur Rahman c A. Perera b Prasad 25
Mominul Haque run out 60
Mushfiqur Rahim c Senanayake b Prasad 30
Naeem Islam c Prasad b Senanayake 32
Nasir Hossain c Priyanjan b Lakmal 38
Mohammad Mahmudullah c Thirimanne b Lakmal 5
Sohag Gazi b T. Perera 23
Shafiul Islam not out 15
Arafat Sunny not out 1
Extras: (lb2, w7) 9
Total (for eight wickets, 50 overs) 240
Fall of wickets: 1-17 (Anamul), 2-62 (Shamsur), 3-108 (Mominul), 4-130 (Rahim), 5-184 (Islam), 6-200 (Mahmudullah), 7-201 (Nasir), 8-232 (Gazi).
Bowling: Lakmal 10-3-24-2 (w1), T. Perera 9-0-39-1 (w2), Prasad 10-0-49-3 (w2), Senanayake 9-0-46-1 (w1), Priyanjan 6-0-42-0 (w1), A. Perera 3-0-17-0, Mathews 3-0-21-0
Toss: Sri Lanka
Umpires: Sharfuddoula Saikat (BAN) and Rod Tucker (AUS)
TV umpire: Anisur Rahman (BAN)
Match referee: David Boon (AUS)