The ECB said it bought €2.67bn (£2.23bn) worth of bonds in the week to December 3, up from €1.97bn the previous week and taking the programme's overall total to €72bn.
The spend was the biggest weekly amount since late June, but remains just a fraction of the €16.5bn of bonds bought in the first week of the programme in May.
The low level cast doubt over speculation that the bank had moved the programme up a gear.
ECB President Jean-Claude Trichet earlier this month stressed that the programme was still in effect, leading some observers to expect a larger tally this week.
"We didn't have any promise from the ECB to do a particular level of purchases, but the view in the markets had been that the ECB had scaled up its purchases to a greater extent, " RBS economist Nick Matthews said.
"There may be some disappointment."
The figures may not give the full picture, however. The ECB adds the caveat that the total may be higher than reported as purchases take 2-3 days to finalise.
The ECB can buy government and corporate bonds under the purchase programme but it has given no further details, such as how much it could spend or how long it intends to buy for.
The purchases are the central bank's contribution to a €750bn EU/IMF rescue package hastily brought in at the height of the debt crisis in May.
Most analysts believe it is concentrating its purchases exclusively on euro zone debt trouble spots Ireland, Greece and Portugal.
The ECB publishes the amount of bonds it has purchased on a weekly basis every Monday.
As usual it will take one-week deposits from banks on Tuesday to offset the inflationary impact of pumping money into the financial system via its bond purchases.