Ketenyl radical (HCCO) is an important hydrocarbon combustion intermediate. The mechanisms and kinetics for the reaction of HCCO (X2A″) with H(2S) occurring on both singlet and triplet surfaces have been studied by a combination of ab initio calculations and rate constant predictions at the CCSD(T)/6-311++G(3df,2p)//CCSD/6-311++G(d,p) level of theory. The kinetics and product branching ratios have been investigated in the temperature range of 297–3000 K by variational transition state and Rice–Ramsperger–Kassel–Marcus (RRKM) theories for the production of CH2(a1A1) + CO(X1Σ+) and CH2(X3B1) + CO(X1Σ+). Our prediction for the primary product CH2(a1A1) + CO(X1Σ+) formation is in good agreement with earlier experimental results. The pressure independent rate constant for this channel can be expressed by k1(T) = 8.62 × 10–11T0.16exp(–20/T) cm3 molecule–1 s–1. For the production of CH2(X3B1) + CO(X1Σ+), the rate constant k2 can be represented as k2(T) = 7.63 × 10–16T1.56exp(–386/T) cm3 molecule–1 s–1. The predicted product branching ratios for the reaction are in close agreement with experimental data as well. We also predicted the heat of formation at 0 K for 2HCCO, 3CCO, and 1CCO by CCSD(T)/6-311++G(3df,2p), CBS-QB3, and G2M; the values are in good agreement among one another. Specifically, the CCSD(T) values are: ΔfH°(HCCO, X2A″) = 42.52 ± 0.70; ΔfH°(CCO, X3Σg) = 91.50 ± 0.54; and ΔfH°(CCO, a1Δ) = 110.22 ± 0.54 kcal/mol.