Antimony (Sb) is an element with a growing concern due to its toxicity, but also because of its criticality. While the impact of Sb mining is documented in literature from China and Europe, still little data is available concerning the environmental impact of Sb mining in Vietnam. This paper presents the results of an exploratory study of mine waste and soil samples from the Mau Due mine (North Vietnam). The chemical and mineralogical composition of the samples was determined as well as the water-soluble and exchangeable/reversibly adsorbed Sb species, and the release of Sb at different pH values was investigated. Antimony concentrations in the mine waste samples (slag and waste rock) were in the range of 191–15,699 mg/kg, while soils were characterized by Sb concentrations in the range of 47–95 mg/kg. In one mine waste sample, the primary mineral stibnite was found. The investigated mine waste samples also contained pyrite, which was not found in the soil samples. The leaching of Sb from all the samples with water was relatively low, as less than 1% of the total Sb content in the samples was released. In absolute values, this resulted in water-extractable Sb concentrations (24 h extraction) up to 430 μg/l, except for an alkaline slag sample, which released 23.5 mg/l of Sb, and the mine waste samples containing stibnite (2.9 wt%), which released 16.6 mg/l of Sb. Based on the outcomes of this reconnaissance study, recommendations for further investigation of the waste heaps around the mine were made, taking into account the protection of health and the environment, and the sustainable management of secondary (waste) resources.