Second language (L2) enjoyment has gained recent interest, but little research has attended to the sources of L2 vocabulary learning enjoyment. Drawing on the regulatory focus theory and the assumption that advancing toward a goal can contribute greatly to learning enjoyment, this study examined the extent L2 vocabulary selves and capacity for self-regulatory vocabulary learning are related to vocabulary learning enjoyment. A questionnaire was administered to two cohorts of 897 low-intermediate university students at two different times: one in the middle of a summer semester and the other in the following semester. The ages of the students were in the 17 to 24 range (M = 18.84, SD = 0.79). Hierarchical regression, dominance, relative weight, and Boruta random forest analyses revealed that capacity for self-regulatory vocabulary learning was the most important predictor of L2 vocabulary enjoyment, followed by ideal L2 vocabulary self/own. Mediation analyses showed that capacity for self-regulatory vocabulary learning had a direct effect on L2 vocabulary learning enjoyment, and ideal L2 vocabulary self had a stronger mediating effect than ought L2 vocabulary self. The findings and implications were discussed.