This paper aimed to establish the species diversity of earthworms (Oligochaeta: Lumbricidae) and the chemical composition of earthworm surface castings within an urban park from west side of Romania (Timişoara City): Plevnei Park (45°44’58’’N, 21°13’38’’E). Eight lumbricid earthworm species have been identified: Lumbricus terrestris, Aporrectodea rosea, Aporrectodea longa, Aporrectodea caliginosa, Allolobophora chlorotica, Dendrobaena veneta, Dendrobaena octaedra, Dendrodrilus rubidus. Based on species incidence, several ecological indicators have been calculated: the constancy of earthworm species in the sampling areas, the Sørensen similarity of sampling points as species composition, and the Jaccard similarity (coenotic affinity) of the earthworm species within the sampled points. The surface castings have been analyzed for the following physical-chemical parameters: pH, total organic carbon (TOC), total nitrogen (N), plant available phosphorus (P), plant available potassium (K), and calcium water soluble (Ca). Because it is not yet clearly elucidated the casting behavior (surface or subsurface) of earthworms, and their feeding behavior, habitat behavior and casting behavior are not always clearly separated traits, and because until now it is insufficiently known how the environmental conditions affect the surface or subsurface casts production in earthworms, or how these conditions determine more than a single casting behavior for one species, there had been difficult to conclude which of the found species is responsible for the surface casting within the studied urban park. To find possible correlations existing between the physical-chemical parameters of the earthworm castings, Pearson, Spearman, and Kendall correlations (p<0.05) were calculated. The study revealed significant positive correlations between these chemical parameters of earthworm castings: pH-K, pH-TOC, and TOC-Ca.