The 60-minute show at 9pm averaged 5.2 million (21.7%) as the eight celebrities - which included DJ Lisa l'Anson, C4 racing pundit John McCririck and feminist author Germaine Greer - entered the famed house.
The opening show was down by 2 million compared to the first show of the previous series in November 2002 when the audience averaged 7.2 million (29%).
C4's audience for the show still represented a strong audience for the channel, which had an average audience share throughout last year of 9.7%. The programme also comfortably outperformed its slot average for last year of 2.7 million.
The series average for Celebrity Big Brotherin 2002, which was won by Mark Owen, averaged 4.5 million, while the previous year, when Jack Dee won, was watched by 5 million across its run.
The C4 reality show outperformed BBC1's unscheduled Tsunami: The Killer Waveswhich aired in the same 60-minute slot. The special on the Asian disaster gained 4.3 million (18%).
ITV1's 90-minute episode of detective series Taggart, also at 9pm, won the slot with a steady 6.6 million (28%) and reached a peak of 7 million (29%) at 9.05pm.
Both BBC2 and Five were left trailing behind. The final part of BBC2's investigative trilogy into the illegal drugs trade, Drugland, ended with 1.3 million (5%) at 9pm while Five's film Big Trouble in Little China, at the earlier time of 8pm, took 1.6 million (7%).
It was a strong performance for C4 throughout peaktime with A New Life Down Under: One Year Onat 8pm drawing 2.9 million (13%) and Jump Britainat 10pm also impressing 2.9 million (15%).
BBC2's one-off The Hairy Bikers' Cookbookat 8pm gained 2.1 million (9%) while a repeat of comedy Men Behaving Badlyat 10pm had 1.4 million (6%). Five's late film Mississippi Burningat 10pm had 1.4 million (10%).
BBC1's Big Cat Weekhas managed to grow its audience in the 7pm slot so far this week. It started on Monday (3 January) with 4.6 million (18%) and last night averaged 6 million (26%) in the face of stiff competition from ITV1's Emmerdale,which picked-up 10.2 million (45%).
The corporation's soap EastEnderswas also back on form at 7.30pm with 11.5 million (49%), after Tuesday's disappointing 6.8 million (28%).
Viewers switched over to ITV1 at 8pm as the police drama series The Billtook 7.2 million (31%) over 60-minutes. The penultimate episode of BBC1's The Dobsons of Duncraigat 8pm had 3.8 million (17%) while Ground Forceat 8.30pm got 3.6 million (15%).
Peaktime shares for Thursday 6 January: ITV1 - 30.5%, BBC1 - 23.2%, C4 - 13.1%, BBC2 - 6.4%, Five - 5% and multichannel - 21.8%.