Objectives: Smoking is a highly prevalent addictive behavior with severe and life-shortening health consequences. This is the first study to evaluate the efficacy of a newly developed imaginal variant of approach bias modification (ABM) (i.e., imaginal retraining) for the reduction of craving for tobacco and actual smoking behavior. Methods: We randomized 345 smokers to imaginal retraining (self-help manual) or a control group (either active control or wait-list control). Assessments were carried out online. The treatment interval was 6 weeks. Craving for tobacco represented the primary outcome. The study was registered as DRKS00016860. Results: Retention was 79.7% with no difference between groups. The intention-to-treat (ITT) analyses were significant for the primary outcome (Visual Analogue Scale on craving for tobacco) as well as subjective reduction of smoking (45.5 vs. 26.4%) in favor of imaginal retraining. In the treatment group, 47.6% performed the exercises at least once. This subgroup (per-protocol [PP] sample) showed a significant reduction in tobacco dependency as measured with the Cigarette Dependence Scale (short and long forms) and the Fagerström Test for Nicotine Dependence relative to controls. Number of daily cigarettes declined to a greater extent in imaginal retraining in the PP but not ITT analysis. A small dose-effect relationship emerged between craving and frequency of performance of the technique. Conclusion: When used regularly, imaginal retraining may reduce craving for tobacco and actual smoking behavior in a subgroup of smokers. In view of the large subgroup that did not read the manual or did not perform the exercises, alternative ways of conveying the imaginal retraining technique should be sought (e.g., demonstration via video clips). To conclude, imaginal retraining may represent a simple low-threshold technique to reduce smoking and assist current evidence-based treatment programs targeted at abstinence. It needs to be tested whether its mechanism of action deviates from standard ABM.