Dietary biodiversity, defined as the variety of consumed plants, animals and other organisms, can be measured by dietary species richness (DSR). This study investigated associations between DSR and diet quality in Dutch adults. Dietary intake data of 2078 Dutch participants, aged 19 to 79 years, were collected by the Dutch National Food Consumption Survey between 2012 and 2016 via two non-consecutive 24-h dietary recalls. DSR scores were calculated based on the total count of unique species consumed per individual over the two measurement days. An overall DSR score and separate scores for fruit and vegetable species consumption were calculated. The Dutch Healthy Diet index 2015 (DHD15-index) was used to measure diet quality. Linear regression analyses were performed to investigate associations between DSR scores and DHD15-index. Analyses were stratified by age and adjusted for relevant confounders. In total, 157 unique species were identified within the investigated food groups. On average, individuals consumed 13 unique species over two days (SD 4.55). For every additional species consumed, the DHD15-index increased by 1.40 points (95%CI 1.25–1.55). Associations between DSR and DHD15-index were higher in younger adults. DSR fruit showed the strongest associations with DHD15-index (β 4.01 [95%CI 3.65–4.38]). Higher DSR scores are associated with higher diet quality in Dutch adults. These newly developed DSR scores create opportunities for further research to explore the implications of dietary biodiversity in Western diets on health and related outcomes.