Accommodation reservation revenue for the third quarter of 2021 was RMB2.2 billion (US$341 million), representing an 11% decrease from the same period in 2020, and an 11% decrease from the previous quarter, primarily due to the reemergence of COVID-19 infections in certain regions in China.
Transportation ticketing revenue for the third quarter of 2021 was RMB1.8 billion (US$282 million), representing a 5% decrease from the same period in 2020, and a 12% decrease from the previous quarter, primarily due to the reemergence of COVID-19 infections in certain regions in China.
Packaged-tour revenue for the third quarter of 2021 was RMB392 million (US$61 million), representing a 20% increase from the same period in 2020, and a 7% increase from the previous quarter, primarily due to the increase of leisure travel demand in July 2021 before the reemergence of COVID-19 infections.
Corporate travel revenue for the third quarter of 2021 was RMB338 million (US$53 million), representing a 20% increase from the same period in 2020, primarily driven by expansion in corporate customer base and an optimized product mix. Corporate travel revenue decreased by 13% from the previous quarter, primarily due to the reemergence of COVID-19 infections in certain regions in China.
Cost of revenue for the third quarter of 2021 increased by 19% to RMB1.2 billion (US$190 million) from the same period in 2020, primarily due to an increase in compensation to customer service center personnel. Cost of revenue remained relatively stable compared to the previous quarter. Cost of revenue for the third quarter of 2021 accounted for 23% of the net revenue.
Product development expenses for the third quarter of 2021 increased by 15% to RMB2.3 billion (US$358 million) from the same period in 2020 and increased by 4% from the previous quarter, primarily due to the increase in product development personnel related expenses. Product development expenses for the third quarter of 2021 accounted for 43% of the net revenue.
Sales and marketing expenses for the third quarter of 2021 increased by 12% to RMB1.3 billion (US$197 million) from the same period in 2020, primarily due to the increase in expenses relating to sales and marketing promotion activities. Sales and marketing expenses decreased by 9% from the previous quarter. Sales and marketing expenses for the third quarter of 2021 accounted for 24% of the net revenue.
General and administrative expenses for the third quarter of 2021 increased by 57% to RMB792 million (US$123 million) from the same period in 2020, primarily due to a reversal of bad debt provision in the third quarter of 2020 for the Company’s travel suppliers reflecting the change in credit risk with travel industry recovery. Excluding the effect of bad debt provision, general and administrative expenses decreased by 8% from the same period in 2020. General and administrative expenses increased by 11% from the previous quarter, primarily due to an increase in personnel expenses, including share-based compensation charges. General and administrative expenses for the third quarter of 2021 accounted for 15% of the net revenue.
Income tax expense for the third quarter of 2021 was RMB95 million (US$15 million), compared to RMB245 million in the same period in 2020 and RMB97 million in the previous quarter. The change in our effective tax rate was primarily due to the non-taxable income of the fair value changes in equity securities investments and exchangeable senior notes.