Understanding factors within college learning environments that can ameliorate maladaptive academic behaviours such as procrastination could contribute to enhancing college students' success and persistence. Thus, the aims of the current study were to investigate: (a) the degree to which facets of the college classroom motivational environment predict college students' academic procrastination after controlling for students' level of conscientiousness (which is a strong predictor of procrastination); and (b) whether academic procrastination mediates the effect of classroom motivational environment facets on course grades. Participants were 223 students enrolled in two four-year institutions (one a Hispanic-serving institution) in southern US. Hierarchical regression analyses indicated that students who reported the presentation of course material in their classes as being more interesting (course situational interest) also tended to report procrastinating less. Furthermore, mediation analyses indicated that the positive effects on course grades of classroom motivational environments (in which instructors were perceived as providing academic and emotional support, promoting mutual respect and task-related interactions among students, and eliciting interest through the presentation of course material) were better explained as mediated by academic procrastination. These findings suggest that providing a supportive college classroom environment to engage students could cause them to procrastinate less and attain better academic outcomes.