The past evolution of precipitation and atmospheric convection in the Western Pacific Warm Pool (WPWP) is critical for global climate changes but is under debate because of its forcing mechanisms. Here, we present a high temporal resolution (~156 years) grain-size record of core MD01–2385 over the last 140 kyr, in offshore northern New Guinea to reveal sediment dynamics as a proxy for precipitation changes. End-member analysis revealed that a two-endmember model was optimal. The end-member 1/end-member 2 (EM1/EM2) ratio could represent the variation in grain size and exhibited significant precessional cycles changes in phase with modelled Niño 3 SST anomaly from a global climate model transient simulation. From these data, we inferred orbital fluctuations in precipitation from tropical western Pacific islands, with general precipitation peaks during the time of perihelion at the boreal autumnal equinox (midpoint from a low to high precession index), corresponding to La Niña-like conditions and vice versa. Comparisons of our new record with published precipitation records showed that orbital precipitation changes in the WPWP are mainly dominated by El Niño-Southern Oscillation-like (ENSO-like) oscillations in the precession band, while the Intertropical Convergence Zone (ITCZ) mainly controls the distribution of precipitation over a larger spatial area.