Thailand is a country in the Southeast (SE) Asian peninsula. The country has been regarded as a transition zone between the Indian and the western North Pacific monsoons. Climate data from the country is a key for advancing our understanding of monsoon climate in the transition zone area. Previously, high-resolution climate signals preserved within δ18O, growth rate, and grey level were successfully extracted from stalagmite NJ-1, collected from Namjang (NJ) cave in the Mae Hong Son province of northwestern (NW) Thailand [Cai et al., 2010; Muangsong et al., 2011]. Present-day climate and cave monitoring in NW Thailand were carried out from August 2012 to October 2013 to investigate the climatic controls on rainfall and stalagmite isotopic properties. The δ18O of rainfall, stalagmite drip water as well as modern stalagmite precipitated on glass plates generally exhibited seasonal response to seasonal monsoon rainfall δ18O. Theses have implications for the use of isotopic composition of natural climate proxies from NW Thailand as a proxy of seasonal climate as well as the study of seasonal changes in moisture trajectories. Among the limited number of tree species suitable for tree-ring studies, teak (Tectona grandis Linn.) trees have great potential for dendrochronology in SE Asia. There are young teak trees growing out a few meters from NJ cave that uptake a common source water of published stalagmite NJ-1. In this study, the unique signals of cellulose δ18O detected in Thai teak were presented. Intra-seasonal and inter-annual variations of tree-ring cellulose δ18O provided detailed insights into seasonal monsoon climate. Comparisons of tree-ring cellulose δ18O with speleothem proxies from the same locality and tree-ring indices from wider geographical areas provide a basis for developing a multi-proxy approach. This is the first study in Thailand with a precise high resolution examination of δ18O in Thai teak as a climate signal, and this is the first preliminary study on a comparison between two natural proxies from a single location. These findings demonstrated the potential of stable isotope climatology from tree rings and stalagmites, and provided an additional basis for seasonal rainfall reconstruction in this region.