Developing ideal amine solvents with a high CO2 absorption capacity and a fast absorption rate is an attractive avenue to advance the amine scrubbing technology. In this regard, diamines bearing one primary and one tertiary amino group (1 degrees/3 degrees diamines) are proposed to be promising solvents for CO2 absorption, which can exhibit the fast CO2 absorption rate of primary amines while maintaining the diamines' intrinsic high absorption capacity. Here, we present a detailed kinetic study of four 1 degrees/3 degrees diamines for CO2 absorption and investigate the relationship between the structure of various 1 degrees/3 degrees diamines and their CO2 absorption rate. Results showed that increasing alkyl spacer between two amino groups within 1 degrees/3 degrees diamines promoted the CO2 absorption rate, while a large decrease in their reactivity with CO2 was observed when the tertiary amino group existed in the cyclic structure. Among these studied 1 degrees/3 degrees diamines, 3-(dimethylamino)-1-propylamine (DMAPA) displayed the highest absorption rate under relevant conditions and also exhibited higher overall mass transfer coefficients than those of monoethanolamine over the entire range of CO2 loadings, and the main reaction routes for CO2 absorption into DMAPA solution via formation of the protonated DMAPA-carbamate were proposed.