TESS has been highly productive in detecting new exoplanets since launch and HD219666b was the first hot Neptune discovered by TESS in sector 1. The high equilibrium temperature (~1000K) and bright host star (V=9.81) make it a great target for follow up atmospheric characterization with HST and JWST. Here we present our preliminary transmission spectra of HD219666b using HST with WFC3 G141 and G102 grisms.