Objective This study aimed to investigate the relationship between the stress hyperglycaemia ratio and haemorrhagic transformation after intravenous thrombolysis in acute ischaemic stroke patients. Methods We analysed data in Shanghai General Hospital from 2019 to 2022 on 161 men and 68 women with valid data on fasting blood glucose, glycated haemoglobin, and cranial computed tomography using multivariable regression models to examine the relationship between hyperglycaemia ratio and haemorrhagic transformation. Results All 229 patients in this study were included, with 161 males (70.3%) and a mean age of 69.0 (SD = 11.3). According to the median hyperglycaemia ratio (0.87), all patients were divided into two groups (M1 <= 0.87). Patients in the M2 group tended to have a higher fasting blood glucose, body mass index, glycated albumin, and apolipoprotein E, while the door-to-needle time in M2 was longer than in M1 (all p values < 0.05). The fasting blood glucose, hyperglycaemia ratio, urea nitrogen, glycated albumin, D-dimer, and the score of NIHSS in the haemorrhagic transformation group were higher than in the non-haemorrhagic transformation group, but the haemoglobin was lower (all p values < 0.05). In the overall population, the hyperglycaemia ratio was associated with haemorrhagic transformation after intravenous thrombolysis before and after full adjustment for age, sex, body mass index, hyperglycaemia ratio, glycated albumin, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, apolipoprotein E, door-to-needle time and the score of National Institute of Health Stroke Scale [OR = 3.34, 95% CI: 1.27-7.76]. Conclusions This result implied that the hyperglycaemia ratio is significantly associated with haemorrhagic transformation after intravenous thrombolysis in stroke patients. The stress hyperglycaemia ratio should be borne in mind after intravenous thrombolysis regarding the incidence of haemorrhagic transformation.