Background: Large amount of financial incentive was effective to increase tobacco abstinence, but the effect of small amount is unknown. Purpose: We evaluated if a small amount of cash incentive (HK$500/US$64) increased abstinence, quit attempt, and use of cessation aids. Methods: A three-armed, block randomized controlled trial recruited 1143 adult daily smokers who participated in the Hong Kong "Quit to Win" Contest. Biochemically validated quitters of the early-informed (n = 379, notified about the incentive at 1-week and 1-month follow-up) and the late-informed incentive group (n = 385, notified at 3-month follow-up) received the incentive at 3 months. The validated quitters of the control group (n = 379) received the incentive at 6 months without prior notification. All subjects received brief advice, a self-help education card and a 12-page booklet. The outcomes Were self-reported 7-day point prevalence of abstinence, quit attempt (intentional abstinence for at least 24 h) and use of cessation aids at 3-month follow-up. Results: By intention-to-treat, the early-informed group at 3-month follow-up reported a higher rate of quit attempt (no smoking for at least 24 h) than the other 2 groups (44.1% vs. 37.4%, Odds ratio (OR) = 1.32, 95% CI 1.03-1.69, p = 0.03), but they had similar abstinence (9.2% vs. 9.7%, OR = 0.95, 95% CI 0.62, 1.45). The early and late-informed group showed similar quitting outcomes. The early-informed group reported more quit attempts by reading self-help materials than the other 2 groups (31.4% vs. 25.3%, OR = 1.56, 95% CI 1.12-2.18, p < 0.01). Conclusions: The small cash incentive with early notification increased quit attempt by "self-directed help" but not abstinence. Future financial incentive-based programmes with a larger incentive, accessible quitting resources and encouragement of using existing smoking cessation services are needed. CO (C) 2016 Elsevier Ltd. All rights reserved.