Epoxidized natural rubber (ENR) is derived from the partial epoxidation of the natural rubber possessing some new properties such as good wet grip, oil resistance, excellent flexibility and low rolling resistance [1,2]. The epoxy group of ENR is unstable that could be utilized for the modification of ENR or being a compatilizer [3,4] in rubber composites. It is well known that SiO 2 is used widely in industry except for carbon black, usually as a reinforcement agent or a functionalized filler to impart specific properties for rubber compounds [5]. In our previous work, The ENR/SiO 2 hybrids prepared by an openmill mixing method had been reported, and the interfacial interaction of ENR and SiO 2 was investigated. The results indicated that the ring-opening reaction of the epoxy groups of ENR chains occurs and the covalent bonds between C-OH of ENR and Si-OH groups on the silica surfaces were formed, which can improve the dispersion of silica in the rubber matrix and enhance the interfacial combination between rubber and silica. However, the hybrid obtained a good strength only with a high content of SiO 2 [6], where the elongation at break of hybrid was limited regrettably. This might be attributed to the insufficient filler-rubber interactions. There are still improvements that need to be made in the elongation at break and processability. Mark and Pan [7] firstly proposed a new approach for preparing silica-filled elastomers by generating the silica particles inside the crosslinked silicone rubber. The sol-gel process brings a good dispersion of the silica filling into the rubbery matrix. In general, the sol-gel reaction of tetraethoxysilane (TEOS) takes place easily and proceeds in the two steps, hydrolysis and condensation reactions, to produce SiO 2 . 180Preparation and stress-strain behavior of in-situ epoxidized natural rubber/SiO 2 hybrid through a sol-gel method Abstract. In this paper, epoxidized natural rubber was reinforced by silica generated in-situ though the sol-gel method using tetraethoxysilane(TEOS) as precursor. The results showed that the ring opening reaction of epoxy group appeared in the insitu reaction progress, where the hydrogen bond between Si-OH and C-OH was mainly formed to enhance the stress-strain behavior of ESH simultaneously. During the hot pressing progress, the compound was crosslinked via the chemical reaction of Si-OH and C-OH. The chemical bond between Si-OH and C-OH reinforced rubber-filler interaction, resulting further improved the stress-strain behavior. Besides, comparing with precipitated SiO 2 filled ENR, the dispersion of SiO 2 in ENR matrix was distinctly more uniform though the sol-gel method, along with the enhancement of mechanical properties. Herein, our findings open up a new way to prepare an environmentally friendly rubber composite with excellent dispersion and strong rubber-filler interaction without curing agent effectively.