Nowadays ever-increasing consumption of fossil fuels due to populate as well as industrial growth has led to serious ecological threats due to excessive emission of greenhouse gases and pollutants. Therefore, using renewable recources as alternative for fossil fuels has been chosen as an important and interesting strategy in recent years. Biomass is among the cleanest and least expensive choice of renewable recources which has been the subject of many researches during last years. Rice straw is one of the most frequent lingocellulosic crop residues which is plentiful in Asian countries especially Iran and case a lot of environmental problems after harvesting the rice for the farm. The problem with using rice straw, like other lingocellulosic feed stocks, is its structural solidity due to lateral bonds between cellulose, hemi-cellulose, and lignin. To further expedite anaerobic digestion and dark fermentation by microorganisms, it is necessary to destruct the crystalline structure through various pretreatment methods. In this study, the effect of alkaline pretreatment via sodium hydroxide followed by nano-titanium dioxide photocatalysis on rice straw was performed in order to increase biohydrogen and biogas yield through dark fermentation and anaerobic digestion. Anaerobic sludge was used as inoculum for anaerobic digestion while heat shocked (15 min at 95?C) pretreated sludge was used for dark fermentation. Rice straw was first pretreated using 3 concentrations of NaOH (0, 2, 4% (w/v)) at three temperatures (30, 60, 90?C). The pretreated rice straw was further hydrolyzed using three concentrations of TiO 2 (0, 0.01, 0.1% (w/v)) under UV irradiation for two time durations (30, 60 min). Dark fermentation was performed for 4 days and hydrogen in gas phase and volatile fatty acids (VFAs) in liquid phase were analyzed. Consecutive production of biogas was studied by addition of anaerobic microbial inoculum to remain of the hydrogen fermentation. All experiments were carried out in 118 ml dark bottles at 37?C for duplicates. Quantitative investigations were done using parameters of total and volatile solids, analysis of biohydrogen and biogas, concentration of the produced volatile fatty acids, and combination percentage of carbohydrate and lignin in solid samples. Qualitative comparison of samples was performed using scanning electron microscopy (SEM) pictures. Total and cellulosic crystallinity were investigated using fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) tests. A significant effect was observed in alkaline pretreatment followed by TiO 2 on rice straw as increasing the surface availability and decreasing crystallinity, as well as lignin removal. The highest biohydrogen production (86 ml/g VS) was occured in the sample pretreated with 4% NaOH at 90?C followed by hydrolysis at 0.1% TiO 2 for 60 min UV irradiation, shows five-fold enhancement compared to the non-pretreated sample and two-fold enhancement compared to absence of TiO 2 . The highest amount of biomethane production (577 ml/g VS) was achieved in pretreatment with 0% NaOH at 30?C followed by hydrolysis at 0.1% TiO 2 for 60 min UV irradiation, which shows two-fold enhancement compared to the non-pretreated sample. Keywords: Biohydrogen, Biogas, Rice Straw, Alkaline Pretreatment, Nano-Titanium Dioxide