Background: Over 1.3 million people in the US are living with CRC. Physical activity is associated with lower risk of CRC mortality. Interventions are needed to increase physical activity after CRC diagnosis. Methods: We conducted a pilot RCT to determine the feasibility (adherence, attrition) and acceptability of a 12-wk intervention using a Fitbit Flex™ and daily text messages to increase physical activity after CRC. Eligible patients had to have colon or rectal cancer of any stage, be disease free or have stable disease, able to speak and read English, and access to Internet and a mobile phone. Individuals with contraindications to moderate-to-vigorous physical activity (MVPA) or exercising ≥30 min ≥5 d/wk were excluded. We explored the impact of the intervention (n = 20) vs. usual care (n = 21) on MVPA via ActiGraph GT3X+ accelerometers pre-/post-intervention. Results: The intervention was feasible and acceptable. On average, participants were 54 y, BMI 28 kg/m² and enrolled 1.5 y after diagnosis; 59% were women, 73% were White, and 61% were stage III. The intervention arm wore their Fitbits a median of 74 d (89% of study days, IQR: 23-83 d) and responded to 74% (34) of the 46 text messages that asked for a reply (IQR: 28-82%). Older participants were more likely to wear the Fitbit (r: 0.72; p < 0.001). Married participants were more likely to wear the Fitbit and respond to texts compared to unmarried (96% vs. 32% wear time, p: 0.02 and 85% vs. 46% response rate, p: 0.006). Most patients (88%) reported that the intervention motivated them to exercise and that they were satisfied with their experience. On average, the intervention arm increased MVPA by 14 min/d, while the control arm increased by only 1 min/d, but there was no statistically significant difference in change in MVPA between groups (mean difference comparing change in MVPA in the intervention vs. control: 13 min/d; 95% CI: -14, 40; p: 0.33). Conclusions: A 12-wk physical activity intervention with a Fitbit and text messages is feasible and acceptable among CRC patients after treatment. Larger studies are needed to determine whether the intervention increases physical activity. Clinical trial information: NCT02966054