The Hang Seng Index fell 0.3 percent, or 70 points, to 28,072.
Turnover was HK$144.9 billion.
Pharmaceutical stocks suffered losses after new rules were issued by the drug regulatory body on the mainland.
WuXi Biologics dropped 8.4 percent, Fosun Pharma fell 8.6 percent and CSPC Pharmaceutical dropped four percent.
Traders remained on edge after mainland officials widened their probe to US-traded Chinese tech firms.
But some tech shares such as Tencent and Meituan rebounded after days of losses, adding almost 1 percent each.
Across the border, the benchmark Shanghai Composite Index dipped 0.1 percent, or 4 points, to 3,530, while the Shenzhen Composite Index eased 0.3 percent, or 7 points, to 2,406. (Additional reporting by AFP)