The Commission said that AliExpress had not properly evaluated whether it had enough people to review the risks and had overestimated the effectiveness of its system in detecting and removing illegal products.
The regulator criticised the company's recommender and advertising systems for exacerbating the spread of illegal products and its reliance on one quantitative indicator to measure its moderation system to prevent the risk of illegal products appearing or reappearing in similar forms.
It said the failure of AliExpress to detect illegal products meant that illegal products ranging from counterfeit products to unsafe toys and dangerous cosmetics remained online for many weeks.
The Commission also took issue with the company's ineffective penalty policy, which resulted in penalised businesses continuing to sell illegal products on its platform.
It said that the mandatory AliExpress "brand authorisation" system – intended to prevent counterfeit sales – was ineffective and understaffed and was easily circumvented by traders selling fake products.
The regulator said the novelty of the DSA was a mitigating factor in calculating the fine, which could have been higher.
The penalty is significantly higher than the €120 million handed out to Elon Musk's social media platform X in December last year and the €200 million Temu was fined last May, both for DSA violations.
AliExpress dodged a fine, which could be as much as 6% of its global annual turnover, in June last year after agreeing to measures to tackle the dissemination of potentially illegal and pornographic materials on its platform.