Ultracold rotational deexcitation cross sections and rate coefficients have been computed for CO collision with proton using close-coupling method on the two-dimensional ground state potential energy surface computed at the MRCl/cc-pVTZ level of theory. State-to-state rate coefficients have been obtained for temperature range from 10(-5) K to 200 K. The system displays higher propensity with j' = 0 cross section magnitude closer to j' =1 state, and j' = 2 cross section closer to j' = 3 state, from initial j = 4 state. In ultracold region, the magnitude of cross section increases with the decrease in collision energy following Wigner's threshold law. (C) 2016 Elsevier B.V. All rights reserved.