Pedogenic carbonates document a wealth of environmental information, but their seasonal variations may obscure long-term trends. Here we report evidence of changing seasonality of pedogenic carbonate growth from the Chinese Loess Plateau during the Quaternary glacial cycles, using the d¹⁸O of pedogenic carbonates (d¹⁸O_c). The glacial and interglacial d¹⁸O_c show negative and positive correlations with proxy-inferred rainfall amount, respectively. We explain this pattern using modern observations and modeling results, which show opposite correlations between d¹⁸O_c and rainfall amount in growing versus non-growing seasons. In glacial episodes under weak monsoon, pedogenic carbonate growth occurred within the growing season, inheriting a negative d¹⁸O_c-rainfall correlation. Conversely, pedogenic carbonate growth likely extended into the non-growing season during interglacials due to intensified monsoonal rainfall, incorporating a positive d¹⁸O_c-rainfall correlation. Our work links seasonal fluctuations of pedogenic carbonates with their long-term records, shedding new light on interpreting this paleoarchive.