Background: As no human data exist, we aimed to determine the relation between ambient temperature and volume of perihematomal 'cerebral' edema in acute spontaneous intracerebral haemorrhage (ICH) among Chinese participants of the pilot phase, Intensive Blood Pressure Reduction in Acute Cerebral Haemorrhage Trial (INTERACT1). Methods: INTERACT1 was a multicenter, open, blind outcome assessed, randomized controlled trial of intensive (systolic target <140mmHg) vs. guideline-recommended (systolic target <180mmHg) blood pressure (BP) lowering in 404 patients with acute ICH. Data on ambient temperature (mean, minimum, maximum, and range) on the day of each participant's ICH obtained from China Meteorological Data Sharing Service System were linked to other data including edema volumes. Multivariable regression analyses were performed to evaluate association between ambient temperature and edema volumes. A generalized linear regression model with a generalized estimating equations approach (GEE) was used to assess any association of ambient temperature and change in edema volume over 72h. Results: A total of 250 of all 384 Chinese participants had complete data that showed positive associations between ambient temperature (mean and minimum temperatures) and edema volumes at each time point over 72h after hospital admission (all P<0·05). All temperature parameters except diurnal temperature range were positively associated with edema volume after adjustment for confounding variables (all P<0·02). Conclusion: An apparent positive association exists between ambient temperature and perihematomal edema volume in acute spontaneous ICH.